I noticed when I have Pandora open in Safari, especially at full screen, the choppiness when switching desktops is significantly increased. Pandora uses Flash.. perhaps that's another reason that causes lag..
You see... they do. I have a 2012 13" MBP, and Launchpad has been relatively choppy for me. That's it- a very, very minor issue that doesn't affect the performance of the system as a whole. But still, if I can fix it, why not? Well, changing the stacks to folders somehow made Launchpad run at a smooth 60 FPS. Weird.
Not me and I actually have the same exact parts. You don't. You don't have 650GT with 4000 switching or Quad i7.
But not trying to war. I am glad it was fixed in your situation and you are trouble free.
This suggestion helped me as well. I also turned off font smoothing, text looks sharper with the option turned off. I found these 2 changes pretty much eliminated all my UI lag.
For browsing I'm using chrome with adblock. I found this combo to provide a very good experience. Facebook is more responsive and very rarely lags.