I installed it yesterday too. I had an issue before the upgrade with my MacBook Pro not booting under Snow Leopard so had to restore from my cloned backup. I then updated all the apps installed on the computer, refreshed the clone and did a second clone just in case. After that it was a case of running the installer, waiting 10 minutes (I have an SSD) and the computer booted up under Lion.
I had a couple of issues with the upgrade. the first was when it came to install Java for use by PS. I think the Apple servers must have been taking a hammering because it hung a couple of times. An hour wait sorted that out. I also had an issue with Parallels not playing with the desktops properly. I had to right click on the icon in the Dock, select Options and specify a desktop for it to work. Finally Chrome does't work properly in full screen mode.
As for the OS itself, I'm not sure about the natural scrolling. I'll stick with it for a couple of days to get used to it. I had to tweak the gestures to get a back swipe in Chrome and Finder. I'm not impressed with LaunchPad. It seems very limited at the moment.
All in all it was the smoothest and best major OS upgrade I've performed. I don't think I'll bother with a clean install, even though I've created a USB boot stick, since it works so well. Today I'm going to try a hack to enable TRIM on the SSD.