A few days of usage and I can testify to liking Lion.
I updated straight away - but as a precaution made a disk image of my snow leopard installation first, in addition to normal TM backup before install.
I have a Mac Book Pro, as does the wife. We are a Mac only household (have been for years) - so aren't affected by Micro$haft compatibility issues, and don't use Parallels. We don't have any Adobe applications either.
The only losses so far for me are really old free applications that use rosetta - in my case, free OCR software that came with our printer, and freewares: GPSbabel, MacTheRipper (personal DVD copier) and MacAnova (ancient statistics modelling program).
Anything native Intel or Universal runs fine as expected, as it says on the tin, in the Lion release notes.
Only bugs I've encountered are a small issue (one time only) importing a photo into iPhoto which ended up hanging up finder - force quit, reboot and try again got over that, plus an install issue with the Xcode update. The Xcode update required a reboot and reinstall (Xcode not Lion) but nothing worse.
Remember to run software update before AND after install to pick up latest compatible software as well as software versions required for upgrade. And kick off the download overnight - even on 10Mb fibre optic cable it takes hours to pull down. The actual install when started only takes 1/2 hour or so - walk the dogs etc.
If you only live in Mac-verse, Lion is a good OSX update (definitely can't complain at £20.99).
Only other thing to notice is time machine will take a long time to catch up - and spotlight goes through a full index cycle, so expect whurring fans for the first half day or so.