After playing around a bit with iPhoto2, I was pleased that it seemed a bit faster, but it was still way too slow. I noticed in the preferences an option to turn off drop shadows and borders on the image icons. After doing that, there was a substantial speed increase. It is so much better that I had just had to submit this hint.

To turn off the borders and drop shadows just go to the prefences and choose No Border under the Appearance section. It makes a huge difference on scrolling and resizing.

[Editor's note: I know I'm breaking my own rule about publishing hints on prefs items, but this is a good one -- disabling the shadows on my machine makes a huge difference in speed; borders don't seem to have any discernible impact. So I've now switched to a black background with borders in lieu of white with shadows; scrolling and resizing are both now very very quick.]