After reading comments that it felt 'snappier' before and after the update, I thought I'd run Geekbench 2 on my MacBook C2D (2Ghz with 2GB RAM) pre/ post to see whether there really was any improvement.
Both times I ran it on a clean boot, with no other apps running, and did the tests twice to make sure I wasn't getting random results.
Pre-update scores: 2665, 2672
Post update scores: 2617, 2659
So you could argue that it's actually slightly worse...
On a happier note, I put a Hitachi TravelStar 160GB drive in the MacBook two days ago, and am reveling in its space and speed!