Seems like the OS hasn't yet fully optimised system after your heavy work last night. It'll sort things out over the next few days. Many of my graphics heavy games are slow the first few times I run them, then they speed up.
Running a maintenance tool such as Cocktail or SterMachine, which will check all permissions, sort out prebinding, clear caches, and other routine maintenance/housekeeping tasks that sometimes don't get done, will also help a lot.
Putting in an extra 512mb or even 1gig extra of RAM will really really help - OSX really needs a gig minimum. If you can't afford it now, try to get it soon.
Hope this helps.