I've been pointing people here:

 - https://askubuntu.com/questions/18641/theres-an-issue-with-an-alpha-release-of-ubuntu-what-should-i-do
 - http://meta.askubuntu.com/questions/871/when-are-questions-about-ubuntu1-appropriate

I think pointing people to those threads would be sufficient. Something like:

"Please note that 11.04 is alpha. See [this question][1] to see what's appropriate to ask, and check [here][2] to see how to get help." or something.

  [1]: http://meta.askubuntu.com/questions/871/when-are-questions-about-ubuntu1-appropriate
  [2]: https://askubuntu.com/questions/18641/theres-an-issue-with-an-alpha-release-of-ubuntu-what-should-i-do