I've been running Lion since it came out. I upgraded my stock HD which had had a fresh install of SL, and I vaguely recall having some performance issues.
I bought a SSD around the same time and installed Lion onto it fresh, and my comp has been running great (15" 2.2 Ghz). My SSD is only 90 Gigs, and I have 28 partitioned to Windows...so it filled up quick. I was experiencing some brief lockups and decided to purge my hard drive to give my self some free space, and ended up having to do a disk repair to get the lockups to stop. Running awesomely now. Super quick boots and still performs damn well graphically (these nvidia 8600Ms are boss! Too bad I needed the logic board replaced several times...). I would say the main downfall is having lots of tabs and programs open (memory....).
I would have already upgraded to Mountain Lion, and I would be tempted to do a fresh install, but I kinda want to just find somebody that has it so I dont have to pay! Also, I am planning to buy 8 gigs of memory from amazon as I've found it for $120 (prices seemed to be REALLY high, and $120 still is compared to DDR3, but it has good reviews and $120 is kinda worth it for 2->8 gigs). I've read a lot about how our comp supposedly only supports 6 gigs, but I don't believe in mixing different sizes of DDR; they should go as a pair! I've also read some recent reports of people successfully installing 8 gigs.
My mac is still going strong, but it has been through a LOT...dead right case fan, intermittent keyboard/trackpad connection, bong spill on keyboard, messed up new keyboard connector, dropped and broke the CD drive (Jap's replaced it for free when I had logic board issue), wires popping out of power magnet, melted third party power adapter, dead battery, weirdly performing third party battery, single pixel width discolored line at edge of screen (still have it, o well). I love this thing though.