Had a BTO 80GB 5400rpm drive in my 12" PowerBook.
This must have been the most silent drive I've ever had! Virtually inaudible. I was very pleased with the noise level.
Although the drive died after 7 months of usage... It was a Toshiba model.
The replacement drive Apple sent me is a Hitatchi 80GB 5400rpm. Go figure.
Although I did not go that route, I upgraded to a 100GB 5400rpm Seagate Momentus 5400.2 instead. Very quiet too. Nice.
Noise-wise go for 5400rpm drives. Although speed-wise they are not all that better than 4200rpm drives. You will hardly notice a difference.
From reports and tests on the web even the Hitatchi 7200rpm 60GB drive does not speed things up that drastically. Boot time speeds up by 1 second or so. File transfers are 10% faster, which of course is nice, but is that worth a 7200rpm drive?
In my book if in doubt go with a bigger size rather than a faster one. I'm happy I chose a 100GB 5400rpm drive over a 60GB 7200rpm one. Especially with the PowerBook's rather slow bus faster drives don't go that much faster anyway.