My iMac was upgraded from SL, I've had just one issue and I don't think it's related to OSX....If I want to use FaceTime, I have to re-boot the iMac. No scripts or clearing of cache will allow FT to connect. Re-boot, and it connects first time. Apart from that the upgrade hasn't given me any issues at all.
My MBA and my MBP are new, so came with Lion installed anyway.