Even if you don't think they will sponsor you (I did not), apply.
Even if you don't think you know enough (I felt that way), apply.
Even if you don't think you are important enough (I wasn't, and am not), apply.
Even if you are a minority, a woman, in the "out" group (I was, and am), apply.
Even if you don't know what "UDS" stand for (Ubuntu Developer Summit), apply.
Even if you don't consider yourself a "developer" (I didn't either), apply!
What's the worst that can happen, after all? Canonical can say no, and then you'll have to attend remotely. But what if the best happens, and they say YES? They told me yes, and flew me to Florida! The travel agents arranged to have me fly in early, so I could spend some time with my long-time friend who lives north of Orlando. (This time, the city is Budapest!)
If you are sponsored, they will work with you, too. Creating a diverse working environment is one of the most important values of Canonical, to make Ubuntu for Humans. So if you have an interest, apply. See Jono's blog post for more information: http://www.jonobacon.org/2011/02/23/ubuntu-developer-summit-sponsorship-now-open/.
This is new; we now have an explicit anti-harrassment policy: http://uds.ubuntu.com/harassment/
Ubuntu-Women has a UDS resource page: http://wiki.ubuntu-women.org/UDS
I've written a couple of UDS-related posts, during and after UDS-N in Orlando last year: Surviving, Thriving at Ubuntu Developer Summits and UDS and You, Wherever You Are