One of the things that I'm not looking forward to about Rails 3 is overcoming the Google Juice of all of the Rails 1.2 and 2.x stuff. I'll know if a code snippet is 3.x or not, but new people won't. I started using Rails right after the release of 2.x, and my first few projects were certainly doing things the old 1.2 way.
Then again, at first, everyone will say "Rails 3" in their titles, so maybe it'll be okay.
I like the new feature that shows the sql for named scopes:
User.published.to_sql
http://edgerails.info/articles/what-s-new-in-edge-rails/2010...