My MacBook Pro's 100 GB disk has been sitting around 85% capacity for a while now (mainly as I have a partition running WinXP via Parallels) and I decided it was time to upgrade. Combination of storage and a suspicion that the lack of space was impeding performance. I have been putting this off for a while as it is a tricky procedure.
I sourced a 250GB Seagate Barracuda drive (thanks Philip), took a clone using SuperDuper and performed open heart surgery. Took about an hour but given local prices to do this are about $150 NZD this seemed like the way to go. It is a little bit fiddly but the instructions by Extremetech are really good. If a Klutz like me can do, pretty much anyone can.
The only thing I would add to their notes is to test booting your MBP from the cloned drive (just hold down 'Option' while booting the MBP and select the cloned drive - just to be sure it works before going through the process) and don't slide out the tabs holding in the RAM. Very tricky to get back in.
Don't spend too much time looking at your disembowelled Mac per the pic above - kinda like looking down while walking a tightrope I reckon. I am breathing a lot easier now everything is back together.
Now I have space to burn and startup and responsive of apps is *heaps* better.