Smooth sailing. Even did a real upgrade, not a "wipe, install and restore" like so many people recommend. Safari 3 is nice. Web developer tools are nice. Unified UI is nice. Time Machine is nice (coupled with external drive, gives me handy local backups on top of the offsite stuff I already do).
\r\n\r\nCouldn't really care less about the Dock or the menu bar. Stacks are OK, don't really love or hate them. Ditto for Spaces. Ditto for tabbed Terminal since I use screen.
\r\n\r\nTrying the switch from Thunderbird to Mail since Mail is finally able to keep up with the huge blizzards of incoming stuff I get several times a day. No strong opinions so far.
\r\n\r\nHaven't really noticed a performance difference; booting is sometimes a bit slower than what I'm used to, but not consistently so. Doing network-based stuff in Finder still sucks.