I have just upgraded my Unibody MBP 13.3 from 160GB to 500GB and I thought I'd share my experience.
Opening her up:
It's a really easy process, careful of the ribbon cable, but I managed to take it out, replace it with a:
Seagate Momentus 500GB 2.5" Hard Drive SATAII 7200rpm 16MB Cache G-FORCE
Which is nice, however I forgot to take off the screws from the stock HD, meaning that when I closed her up and turned her over I heard a lovely clunk, as the new drive wasn't secured, so be careful of that (rookie mistake).
HOWEVER
Just to let you know, although the drive states that there's only a 0.2Ah increase in power consumption, it gives you a much bigger hit on your battery. Even though the performance is better, I'm not sure it's worth it.
So there you have it, in case anyone was interested
Opening her up:

It's a really easy process, careful of the ribbon cable, but I managed to take it out, replace it with a:
Seagate Momentus 500GB 2.5" Hard Drive SATAII 7200rpm 16MB Cache G-FORCE
Which is nice, however I forgot to take off the screws from the stock HD, meaning that when I closed her up and turned her over I heard a lovely clunk, as the new drive wasn't secured, so be careful of that (rookie mistake).
HOWEVER
Just to let you know, although the drive states that there's only a 0.2Ah increase in power consumption, it gives you a much bigger hit on your battery. Even though the performance is better, I'm not sure it's worth it.
So there you have it, in case anyone was interested