I upgraded my MacBookpro to OSX Lion today. It's $30 in the App Store (or copy the DMG from someone who paid and it's free). ArsTechnica has an extremely comprehensive review of Lion if you want the full details. Here are a few minor hiccups I ran into:
• Custom symlinks in /usr/bin were removed. So far I've noticed the symlink for Git missing (/usr/bin/git -> /usr/local/git/bin/git), I put it back. (There's also a StackExchange thread about this.)
• The AFP protocol on my ReadyNAS - which I was using, among other things, for Time Machine backups - is not compatible with Lion. Fortunately the Netgear folks are quick and have a new beta release with the new protocol; I installed that it seems to be working fine.
• I turned off the new mobile-inspired "natural" scrolling. It doesn't feel natural to me, and I don't want to get disoriented every time I use someone else's computer.
• The new (also mobile-inspired) bouncy scrolling is slightly annoying too, but I can't figure out how to disable that.
• The OS seems to handle memory much better. I'm running all the usual apps, but it's turning a lot more of the "active" RAM (yellow in Activity Monitor) into "free" (green) RAM. I'm not sure what the overall performance impact is yet, but it's nice to see the OS [apparently] cleaning up dead memory better than before.
• Some of the startup items in my user account were removed, I put them back.
Otherwise it's been pretty smooth. I like the new Spaces+Exposé hybrid called Mission Control. One of the main reasons I upgraded so quickly was the new full-disk encryption built in, which I'll set up as soon as I can reboot.