I used to have a 5400rpm, 80 GB hard drive in my Vista laptop. After a year and a half of new software, and gunking up the hard drive, I had only 10 GB of space left, which made my laptop pretty slow.
I popped this 7200rpm, 320 GB hard drive in, and reinstalled from the factory image. WHAT A HUGE DIFFERENCE! No problems at all swapping it out. It boots up in half the time it did when new with the smaller hard drive. Now I have 4x as much space, which is room enough for two partitions (one for programs/OS, and one for data only).
Also, I have noticed about 50% longer battery life, and noticeably cooler operation when sitting on my lap. Operates noticeably quieter.