I having more small yet significant problems with OSX Lion. I'm running the latest version - 10.7.1 - on both my MacPro and MacBook.
I find that I frequently lose the ability to resolve DNS names. This is only resolved by restarting the machine. Some Googling suggests that this issue may be due to a failing mDNSResponser process. I use this machine as a media server, so in practice I get up in the morning and try to tune some Internet radio only to find that I need to reboot my media server before I can do so. I'm going to try killing the process so that I don't have to restart the machine each time.
Sometimes my MacBook just won't sleep. Closing the lid, Cmd-Alt-Eject, and the Apple menu option have no effect. It's really frustrating. Some people report that this can happen if Internet Sharing is enabled - it's not in my case. Apple's 'sleep' implementation used to be its crowning jewel. Coupled with OSX's stability I could: go months without rebooting my laptop, have a working system within seconds of opening the lid, happily sling my MacBook into a bag just moments after shutting the lid. I can't anymore...
When I wake this machine from sleep - when I can actually get it to sleep that is, I often find that the wireless card is in an unknown state. This makes it impossible to connect to a wireless network or switch the wireless off. The machine seems to sort itself out after a few minutes but it's quite annoying - especially if I'm trying to look something up in a hurry.
Summary: With this extremely poor OSX Lion release Apple has reminded us what it was like to run Windows XP on a cheap laptop in 2002.