I clean-installed Lion on my MBP (mid-2009) when it was first released, ran it for a couple of weeks, and reverted back to Snow Leopard due to overall slowness (among other issues). Last night, I chose to take the plunge again, and did the clean install, this time of 10.7.1 (the current version). I also chose NOT to enable the FileVault full disk encryption. I've noticed, this time around, that Lion flies. Mission Control is smooth, the dock is smooth, etc. It may even be faster than Snow Leopard. Of course, this may be due to the 10.7.1 update, but I have not heard of that improving performance much. If anyone is still having lag and performance issues, I suggest disabling FileVault (despite how awesome of a feature it appears to be) and see how that works out.