Finally, I couldn’t wait for the final release to install Ubuntu Hardy Heron. And, at first impression, Hardy seems to run smoother than Gusty, even if I found some minor issues.

Hardy with the same usual applications running seems to eat 10% less memory than Gutsy, all applications open really faster, and there was no issue at the install. these are the really good points.
Gnome 2.22 also brings cool improvements which are described here already.
After a night of use, I’ve seen some (small) issues :

• Many firefox extensions are not yet compatible with firefox 3.
• f-spot is now the default photo manager, my default was gthumb (which is still in the repositories). Tough I’ll give a try to f-spot
• Audacious segfaults (crashes) when launched (beta feeling)
• …

edit : As bapoumba said in a recent post on her blog, there is a thread from frodon that lists known bugs with workaround, check it if you have some issues.
After a month using hardy, I feel it like it is more a RC than a final version, I hope the next release 8.04.1 (which will be released in july) will fix most of the bugs and glitches.