We use it for our staff wiki at both of our companies. We've tried wikis before but found they were lacking in usability, particularly the problem with keeping it organized.
That's a better problem than having the whole domain name be hard to remember. I guarantee you a lot of people will look at this site and go, "Holy cow, that name is total nonsense," because the two doubled letters in a row make it no longer resemble the word "jump" so much as a cat walking on a keyboard. Personally, my skim-reading more closely associates it with the word "app" than "jump," which makes me want to read it as "jumapp."
My personal recommendation: For maximum readability, consider something like "letsjump.in". If you're attached to a quirkily spelled "jump in", "jumpp.in" is fairly readable.
Incidentally, I agree with all of the above commentary. Unfortunately, it's the sad reality of trying to start up an online service/product/whatnot today.
For the canonical, I like letsjump.in or gojump.in - and it's never too early to try and snag jump.in (the owner might be willing to part with it for less than you think). Good luck!
thanks everyone for taking the time to comment. I think the main lessons are:
1) provide independent login
2) explain better what facebook connect is used for
3) provide more information upfront what the service is like, some people can decide if they want it.
4) an example page
i am glad i got early feedback :) thank you all so much