Overall, it's very nicely done, IMHO. A few specifics:
Your dodge around facebook's "no more than 10 invites at a time" is clever.
That said, your app has the good fortune of being inherently viral -- users that want to collaborate with friends will invite those friends. As such, I would recommend toning down the requests to users to invite their friends. It comes off as being too pushy (to me).
It's quite plain-looking, which is normal for a word-processing application but out of place for a Facebook application. I would err on the side of fitting in with your context -- add more icons next to functions, etc.
I just added an icon next to the edit link. I agree it does look plain. I agree that it is too pushy, but until its got self-sustaining growth, they stay there...
It's up to you, obviously, but I found the pushiness extremely off-putting. You need to decide whether the core user activity is writing documents or inviting their friends. If it's writing documents, get rid of the invite clutter. If it's inviting friends, well, good luck, but the app is gone from my profile.
Very nicely done implementation. It works as advertised and everything is absolutely intuitive and straight forward. I don't have much of a use case for it myself though.
At first, when I saw "Friend's Documents" and "My Documents", I thought this was like a native Scribd for Facebook. Which I think could be an interesting idea...
If you are a facebook app developer, your ears should perk up when people say things like "what's the use case?" or "why would I use this instead of xxx?". I think the general solution is to have a good answer to the question, then tell your potential users about that answer -- for example, on the application description page. "Collaborate easily on class projects! Write a story with some of your friends!" Or whatever.
I didn't mention it in what I said, but I don't think I would use your app either -- which I guess is the ultimate question, the one that matters.
Your dodge around facebook's "no more than 10 invites at a time" is clever.
That said, your app has the good fortune of being inherently viral -- users that want to collaborate with friends will invite those friends. As such, I would recommend toning down the requests to users to invite their friends. It comes off as being too pushy (to me).
It's quite plain-looking, which is normal for a word-processing application but out of place for a Facebook application. I would err on the side of fitting in with your context -- add more icons next to functions, etc.
Congrats and good luck!