I was in MassChallenge '10 and it was a great experience. One big difference between MC and most incubators is that it's a non-profit. You get free office space, access to a great set of mentors, and, if you're one of the top teams, you get a share of $1m. Everything, including the money, is non-dilutive and comes with no strings attached.
I was in LaunchBox DC (which has since moved to NC Raleigh/Durham area) it was a very positive experience. The advisors brought in great connections: Steve Case, Tim O'Reilly, various startup CEO's, etc for weekly round table discussions and advice.<p>The overall outcome was a third of the class ended up either getting acqui-hired or taking additional investment, a third is still bootstrapping, and everyone else scaled things down to a side business or just faded away.
Kincast is in Sproutbox <a href="http://sproutbox.com/" rel="nofollow">http://sproutbox.com/</a> right now. The experience has been great. You instantly get a great UX person, designer, and a few developers without having to recruit and hire people. You don't get lots of cash, but the instant access to more engineering resources is very nice.