I'm using Solidworks 2011 and have found that there is a noticable lag while tabbing between open Solidworks documents.  I can count to 4 or 5 before the window changes.  With 2010 there was no lag.

My system is XP Pro with all updates (I know...) running on a dell precision 380 with 4gig of ram and an Nvidia Qudra FX540.