Great thread, there is so much confusion around the internet about replacement harddrives.
Me myself, I swapped a stock 5400 120 gb Samsung for a 7200 WD 320 scorpio black in my 2007 SR MBP. The speed increase is inmense (despite the SATA 1,5 limit), with no noticable additional battery drainage.
However, the stock HD is dead silent and doesn't vibrate the slightest. The WD vibrates a lot, althou not much louder than the fans at 2500 rpm, but I can hear it, especially on a wooden surface. Also, at completely random occassions the hard drive suddenly bleeps somehow. I have yet to find a reasonable explanation for this phenomenon but I grew over it.
This weekend I'll try to isolate the WD completely with very thin rubber strips, lefover from some desktop HD's, on all sides. I'll post it if that completely solves the vibrating problem