This is going back a few years to my old 500MHz TiBook which came with a 4200 rpm 20 GB HDD and which I swapped out for a then top of the line 5400 prm 40 GB drive. The difference was decidedly noticable particularly (obviously) booting but also general performance. If you are adept with a screwdriver it should not be too tricky on the new PB's and OWC do some good deals. I got a firewire case with the new drive and then used Carbon Copy Cloner to dupe my internal HD to the external drive and then swapped them over, it worked a treat. I'm thinking of doing the same as you with my 17" PB now. As far as I know there are no 2.5 inch drives bigger than 100 GB at the moment, I just wish that someone would do a 100 GB 7200 rpm drive.