The updated Ubuntu 11.04 "Natty Narwhal" release schedule is available on the Ubuntu Wiki. I say updated because the release schedule was already available for some time, but it had to be reworked because Ubuntu 10.10 Maverick Meerkat will be released on October 10 and not at the end of the month like it was originally planned.
Update November 3rd: The Ubuntu 11.04 release schedule has been modified so I've updated the post. Initially, there were supposed to be 5 alpha versions of which the first was supposed to be released on November 4th.
Update February 11th: there will be no Ubuntu 11.04 RC and instead, a second beta will be released on April 14th (instead of 21st).
Here is an overview of the Ubuntu 11.04 Natty Narwhal release schedule:
- December 2nd - Alpha 1
- February 3rd - Alpha 2
- March 3rd - Alpha 3
- March 31st - Beta
- April 14th - Beta 2
- April 28th - Ubuntu 11.04
A detailed Ubuntu 11.04 Natty Narwhal release squedule can be found @ Ubuntu wiki.
Target Versions for Release
x-server: 1.10  (Feb 2011)
mesa: 7.10 (Dec 2010)
libdrm: 2.3.23  (Dec 2010)
Thanks to: Starks for the target versions info | Ubuntu Dicas for the Ubuntu 10.10 release schedule heads up!