I have had the occasion to install Lion twice, due to the lucky misfortune of having my 2009 i7 inexplicably crash and die, only to be replaced by a 2011 i7 (yay Applecare!) that wasn't Lion preinstalled. Here's what I've noticed both times: after the upgrade to Lion, there were major glitches and bugs. Both times after repairing disk permissions and restarting, the major glitches and bugs were gone. I HIGHLY recommend running disk utility after upgrading to Lion. Today as I was checking to see if TechTool Pro 5 had finally been upgraded to run on Lion (it hasn't) I came across this article - TechTool Pro Brings OS X Lion to a Crawl. After uninstalling TechTool Pro 5 Lion is super snappy. Applications are opening faster, gestures seem more responsive... This is more like what I thought a 64-bit OS would be like. Of course ymmv. I just thought I'd throw that out there in case it might help someone else.