Update, 7 August 2009: the most recent major release of Emacs (v. 23.1) now has the anti-aliased font support. See the Ubuntu elisp PPA, which contains packages for any recent Ubuntu release, or see installation instructions for various other platforms.
The latest emacs-snapshot-gtk packages in Ubuntu Hardy (1:20080228-1) have the Unicode/font changes merged, and now support anti-aliased fonts for the first time.
While I didn't really mind the old bitmap fonts, I have to say that anti-aliasing is gorgeous.
To activate the new fonts, I added the following line to my ~/.Xdefaults:
Then, I ensured that the settings in .Xdefaults are being loaded by adding the following to my ~/.xsession:
if [ -f $HOME/.Xdefaults ]; then
xrdb -merge $HOME/.Xdefaults