I am running Aperture 1.5.2 on my 17" PowerBook with 2GB RAM. There has been no speed issue, display issue, nor any "hangs". The only speed issue I have experienced is on my external USB 2.0 hard drive. That is really slow. I had a Lacie D2 which crashed. I pulled the Maxtor hard drive from inside and installed it in a USB case, etc. Going from FW 800 to USB II is a real downgrade, but $$$ talk and I did not get another FW drive.
I attended the hands-on session for Apple in Boston and feel that Aperture is the best damn DAM on the market now.