A couple of things I’ve noticed on my Mac of late:

• BBEdit was starting up very, very slowly. I threw the BBEdit Preferences file in the Trash; now BBEdit starts up very, very quickly.
• You can now import Firefox bookmarks into Safari. Perhaps you could always do this? I’m not sure. But it’s as simple as File \| Import Bookmarks and then locating the Firefox bookmarks file.
• So far I’ve had absolutely no troubles post-Tiger upgrade other than a general sluggishness of the system (which seems to be getting better). All of my applications and devices are working as they did pre-upgrade.