I've installed it to 4 macs at home and other than few kinks (reversing the default gesture scroll direction, wtf?) everything has gone very smoothly. I haven't noticed any performance issues compared to Snow Leopard. The slowest systems are two 2007 MBP 17" with 2.4 and 2.6GHz C2D and they're perfectly fine. I'm mostly interested about the new security features Lion brings: There are some major fixes inside Lion in this regard. I haven't yet upgraded my work MBP though, since it uses Symantec Full Disk Crypto which is known to have serious issues at system upgrades. Better wait for some other guinea pigs to sort the issues out first... ;-)
BTW: On some systems with fast disk I/O (ones with SSD basically) the initial Spotlight indexing might slow the system to crawl. This happened with my MBP 13". Just wait until the indexing is done and it'll be okay. Of course it's also possible to disabled the indexing altogether if you don't need it.