Okay, I have a Core 2 Duo Macbook Pro with 4 gigs of RAM running 10.7 which is the "recommended" spec for Aperture 3. To my dismay, it would beach ball forever with a ton of threads vying for 100% CPU usage. I have about 40 gigs of photos, most of them RAW and about 10-12 megs each. There is some heft to that, but nothing that justifies waiting for twenty seconds a a time to drag a photo to an album.
After some Googling around, I found the following steps useful in making Aperture run quickly:
Now that I have done both of these things, I can tap the right arrow to browse through my photos at the rate of about one per second which is quite an incredible increase. Enjoy.