I just upgraded the memory in my 15" AlBook from the stock 2 x 256 to 2 x 512. It really zips now. Programs open much faster. Obviously, OS X takes a lot of memory just by itself. Word and Photoshop did not previously open with the speed they now have.
I purchased my book off of the shelf, so I know that the memory upgrade cost me a little more, but my continuing gratification with this powerbook overcomes the bto wait.
I purchased through Ramjet yesterday and the new memory chips were here in Boston this morning.
Gotta love it!