One of the suggestions for play was this move:
- Click Here To Show Diagram Code
[go]$$B
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . 1 . . . |
$$ | . . . X . . . . . , . . . . O , X . . |
$$ | . . . . . . . . . . . . . O X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
This move has benefit in that it hits a key shape point for both sides: black's shape is good, and it keeps white from taking this point, which would help white's shape a bit.
It is important, however, to consider the reason you might play this move from a global standpoint. Looking at a "normal" joseki, under what circumstances does black play this move?
For example, here's a common local joseki:
- Click Here To Show Diagram Code
[go]$$B
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . 5 . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . 4 . O , X . . |
$$ | . . . . . . . . 6 . . . . 2 1 3 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
It's even - white gets a position on the bottom, and black gets points. Great, right?
But let's consider a board position where black has some solid stones up top:
- Click Here To Show Diagram Code
[go]$$B
$$ ----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . O . . |
$$ | . . . , . . . . . , . . . . . O . X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . B . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . B . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . B . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . O . O , B . . |
$$ | . . . . . . . . O . . . . O X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
Above, the marked black stones are very low. Black has invested stones on the right, and he can't really develop there - his stones aren't doing that well together. Black could consider a pincer or something else in response to the 3-4 approach, but there is another way of playing, which is also joseki:
- Click Here To Show Diagram Code
[go]$$B
$$ ----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . O . . |
$$ | . . . , . . . . . , . . . . . O . X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . C C . |
$$ | . . . . . . . . . . . . . . . . C C . |
$$ | . . . . . . . . . . . . . . . . C C . |
$$ | . . . . . . . . . . . . . 5 . 7 . . . |
$$ | . . . , . . . . . , . . 4 6 O , X . . |
$$ | . . . . . . . . 8 . . . . 2 1 3 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
Note black 5 and 7, above. These stones have a drawback compared to the earlier joseki: the marked area isn't yet solidly enclosed, so if white invades later, black might not get the territory. But the benefit of these stones is that black is no longer so low on the right, as he is in the earlier joseki. His stones are balanced, and he has potential for development. To be sure, white can still reduce (eg. shoulder hit), but the high stones working together with the 3rd line stones offer more than all 3rd line stones on the right. That's at least one of the powers of this joseki.
This brings us to the discussion at hand of the weird joseki deviation by white. Supposing the board position is similar to above, where black wants to maintain some sort of future potential, it might make sense for black to want to play the diagonal move instead of the more territorial joseki:
- Click Here To Show Diagram Code
[go]$$B
$$ ----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . O . . |
$$ | . . . , . . . . . , . . . . . O . X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . 4 . 5 . . . |
$$ | . . . , . . . . . , . . . . O , X . . |
$$ | . . . . . . . . . . . . . 2 1 3 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
But this doesn't quite work as well in relationship with the stones on the right as the joseki does. In the joseki, black gets stones both at the locations of

and

, above. But above, black only gets

. To be sure, white is at disadvantage locally, because he deviated from the joseki, and the bottom can't turn out great for him.
But the point, in my mind, of

, above, would be to offer development on the right - and to that effect,

hinders this development.
In the above position, I don't think playing low would be good either, for the same reason discussed earlier. Probably just something simple to benefit locally. For example, since black is solid above, this would seem OK for black to me:
- Click Here To Show Diagram Code
[go]$$B
$$ ----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . O . . |
$$ | . . . , . . . . . , . . . . . O . X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . 8 . . |
$$ | . . . . . . . . . . . . . 4 . . 6 7 . |
$$ | . . . , . . . . . , . . . . O , X . . |
$$ | . . . . . . . . . . . . 9 2 1 3 . . . |
$$ | . . . . . . . . . . . . . 5 . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
This all being said, it is probably still better to play this way:
- Click Here To Show Diagram Code
[go]$$B
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . 1 . . . |
$$ | . . . X . . . . . , . . . . O , X . . |
$$ | . . . . . . . . . . . . . O X X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ----------------------------------------[/go]
instead of playing on the 3rd line in a situation like the one above. But I'd rather not play there at all, since black doesn't get as much development potential on the right than in the joseki.