Wow, this sounds like me. I've been using Lion since the first DP, then I decided to go back to SL because it was buggy. But then as soon as the gold version hit, I upgraded and never looked back. I thought I was following the natural course - when a new OS is released, most people generally upgrade.
I was happy with Lion - it was decent, I never had any WiFi problems. Mission Control took a while to get used to, but it wasn't the worse thing ever. The lack of all windows Exposé, however, was. But alas, time to move on, and I forgot all about it.
Then, after about 8 months, I start to fire up some VMs, 'cos I needed to run Windows, and noticed how slow it was. I thought it was because I didn't have enough free space, so I went ahead and deleted some files. No go. Then I start reading all the complaints with Lion that people had - battery lasting less, terrible RAM management, lack of Exposé/Spaces which JUST WORKED (Mission Control is a disaster for more than 4+ desktops, I tried it).
And then I decided to downgrade, in early March of this year. I stayed with SL for two weeks, but it felt awkward, 'cos I was used to the whole gestures and MC with Lion. Plus, iCloud and iMessages. I thought: 'wow, I need iCloud!' so I decided to do a zero-out and install Lion CLEAN.
First day, it was much faster. Wow, a clean install worked wonders. But over time, it started to page out my RAM. I used Lion for around a month (end of March - end of April). I tried disabling dynamic_pager, that worked, but then as soon as the Mac started to have very little free RAM, it would freeze temporarily. Nah, that's not good enough.
Back to Snow Leopard - and can you believe it, everything just works: longer battery performance (and mine already has 1,015 cicles - it lasted 1h to 1h30 on Lion, on SL it's over 2h), Spaces/Exposé again (rejoice!), decent RAM management. I'm a happy camper.
My Mac is a 13" mid-2009 model, 2.26 Ghz with 4 GB RAM. I might upgrade to ML this summer, but I'll need 8 GB and A LOT of patience.
Same thing happened to me. Same model machine. Also, I noticed when on Lion, animations weren't totally smooth (I have a MacMini 2011 i5 and Lion is perfect on that machine, animations smooth) and I could hear a light sort of "clickwheel" noise when scrolling in Safari and when toggling in and out of fullscreen. I'm assuming it had something to do with the graphics? A bit of a shame actually, because I enjoy Lion, save for a few things - but I would return to Lion (and, in turn, ML this summer) if I could.