I don't suppose we could all maybe come together on this one to put an end to this Lion is Vista nonsense? Huh, just this once, please?
Vista on release was awful with fundamental problems including, but not limited to, system instability, a crippling lack of drivers from crucial hardware partners (like the major GPU vendors for a kick off), crippling performance issues (file transfer chief amongst them) and was generally a far, far worse OS than the one it was intended to replace.
Lion, by contrast, is possibly the most successful big OS launch from the main vendors I can remember since.... well, I'm struggling actually. Windows 7 was good out of the box but there were still a fair number of common problems (albeit that's not really a fair comparison thanks to the plethora of hardware W7 has to work on compared to the limited systems that OS X deals with). Lion hasn't (thus far and fingers crossed) run into any major problems, the common problems seem to be almost exclusivley related to third party software and hardware and the usual complaining about features changing and thus disturbing the balance of the force. Heck, just look at the first page of the Lion forum right now, not one single thread other than the sticky and a poll is over 3 pages long and I think I'm right in saying all multi-page threads are opinion pieces. That's remarkable. Reviews are genrally positive across the board and the reviews in the mac app store are incredibly high considering the usual tendency to rank software down if it doesn't include a free unicorn.
As for the specific problem the OP has, GGJstudios's suggestion of looking to see what's hogging the memory would indeed be a very good place to start.