It boils down to following the instructions on extremeTech.com. The most difficult thing was finding a Torq 6 screwdriver - one of my mates had one, after striking out in the local hardware stores. Took about 45 minutes, and a little bit of wrestling with the keyboard/lid. Now I've got a 200gb instead of 160gb, and more importantly a 7200 rpm and 16m cache drive instead of a 4800/8mb. Its a bit snappier, for sure. Eclipse and Notes 8 especially.
After doing hard disk swaps on PC's, I was expecting a world of pain in terms of imaging the disk. Nope. SuperDuper! did a fantastic job of initialising, imaging and making the disk bootable.
Its true you know, its just easier on a Mac.