Originally Posted by Photo Tramp 
The more RAM you can give your computer the better it is for any Adobe product. Adobe is a memory hog and has always been. Know this, (the more pictures you add to Lightroom the slower it will process) If you can add additional memory do so and light room will eat as much as it has to to function.
I put a 4HD striped RAID array onto my machine just for Photoshop/Lightroom. Memory is maxed out at 4GB (XP-Pro won't address more than that). I was finding that things really slowed down when I ran out of RAM and was into the swap drives, so it seemed like a good idea.
It definitely speeds things up.
Also make sure that the swap drives for Adobe are not the same drive as your operating system swap drive.
And, if you are putting more than 3gb of RAM into your machine, make sure you use the /3gb switch in your boot.ini file (Windows XP users).
With Lightroom, I have the primary catalog on the striped drive, and am backing it up to a mirrored drive.