When doing kernel development, I often run recursive diff on a pair of similar kernel trees. With 768MB+ of RAM, both trees get cached, and subsequent diffs are VERY fast. With only 512MB, there's some thrashing, and the diffs take much longer.

For the Hijack kernels, I've stripped the trees of unneeded architectures, so that my 512MB laptop machine can diff them from cache.

My only other big motivation for more memory, is running VMWare. It can pretty much chew up whatever I throw at it. I imagine that virtualization programs on the Mac platform would benefit similarly.

Lacking the need for either of those scenarios, I imagine 512MB would be fine for today's stuff.

Cheers