These days mine usually swap in a second or 2,
I'm running Ultimate Vista x64 without the aero crap to avoid crashing videocard drivers.

When I was still running on the aero theme it was a lot slower aswell,
What also slows it down is visiting a few busy zones, the effect stays, even after zoning into an instance or such.
And when I play for an entire day (my usual sunday) It gets slower after a few hours.

I started to exit the game every few hours and restart all my wow installs,
especially when i'm editing my ui, I've had enough crashes while editing them and every time I lost half my progress.