My applications used for Go Study and practice:
Dropbox

What is it used for? Transfer file from and to computer without connecting the iPad. Can also be used to share among users. Compatible with Smartgo Pro and Tengen Go.
How could it be improved? Pretty solid application. Not much to say, really.
Smartgo Kifu
What is it used for? It's a must have. The problems are very nice. The pro game database is excellent and very complete. You can import/export SGF, add comments, review annoted games in an easy way, play on the device together with someone (recording the moves) and play against the computer (I put it last because I never do).
How could it be improved? It is wonderful but there is still room for improvement: I wish you could create set-up in a similar way as Drago does (place stones by color to create sitution without alternating colors)), I wish you could add problems, I wish you could manage directories of your file to ease cluster and review. I wish you could set a timer for face to face games. I hope some of those wishes come true as the software develops.
My Library
What is it used for? List all my go books in a database with covers (I love the feature when you can browse your library through covers), authors, barcode numbers, publisher, etc. Good to go for a purchase and not forget which collection you want to complete (if like me you buy books faster than you read them). You can also follow what you did read and comment them.
How could it be improved? Change the logo on the first page (so blurry), export covers would be nice, shared database with comments from other people, more go books in the barcode ref. database.
WebOffline

What is it used for? My iPad is wifi only. This allows me to record some websites to be reviewed at a later stage.There is a kind way of doing by browsing the site and recording and a more brutal way of recording pages at a certain depth (don't try this on sensei's library => your IP would get blocked).
How could it be improved? It's fairly good. Nothing blatlant.
BlogPress

What is it used for? To feed a blog (by Blogger). It's really not as nice as doing it online which I believe you could partially do through a normal browser but it's quicker.
How could it be improved? Implement all features available on site (especially related to the images), add a preview function because WYS is not always WYG.
Max Journal

What is it used for? Follow up my progress on the game on a day by day basis. Make notes following my go lessons. Includes images.
How could it be improved? Improving the export to PDF (use the fancy fonts that are available)
Good Reader
What is it used for? read and organize PDF. Can be used to bookmark, make notes, etc.
How could it be improved? Color notes, read all PDF (example: the Cho Chikun L&D serie is not readable...)
Crop Suey HD

What is it used for? crop images to add to the blog, journal, mind map or library.
How could it be improved? It does what it's supposed to do. It's not very expensive and is very straightforward. Still, I believe you can find free equivalent. This one is just fast which is nice.
Popplet

What is it used for? A mind mapping tool. I like to record go principles, books read, comments in a graphic way. I think it's easy to review and it looks so good. Try the lite version as you may not share my enthousiasm if it's not your taste.
How could it be improved? A few more features, ability to export file into a modifiable format on PC. Still I love the easy and graphic way of creating / move things. I'm a bit unsure about the best way to use it for go study but still love it.
Igowin HD

What is it used for? Play against the computer in 9x9 and see your rank improve (or stagnate - I can't believe that this program is so accurate in assessing your level)
How could it be improved? integrated go courses to win in 9x9...
Tengen Go

What is it used for? Play online on IGS. As KGS is sadly not available, that you're only way to play online real time. It works nicely but it crashes from time to time if you try to do fancy things. Lately, it has became able to record games and export SGF : this is nice!
How could it be improved? Correct the bugs ! At least, it's a beta version : there is good chances that it will get better as times goes by
Boardz

What is it used for? Play online in turn by turn.
How could it be improved? It is nicely programmed. It involves more games. As far as go is involved, it's very nice (especially now that a chat has been created). Still, I don't play it so often.
BG Timer

What is it used for? Time games. It includes bio-yomi and canadian bio-yomi.
How could it be improved? Well, i think this kind of feature is nice on a cell phone but an iPad for this purpose looks a bit heavy and not that much practical. I guess that if you don't have alternative, it does the trick.

Must have application

Recommended

Nice to have

Could do without

Not recommended
What about you? What applications would you recommend for extended go study / practice?