The upgrade process is relatively easy and does not invalidate your warranty. Sony even provide info on how to do this in the PS3 manual.
All you have to do to upgrade your hard drive is the following:
- Back up hard drive (optional if you want to keep your downloads and game saves)
- Turn off PS3
- Remove hard drive
- Insert new hard drive
- Turn on PS3
- Restore backup data (optional if you want to keep your downloads and game saves)
It's all very simple indeed. All your log-in data, internet settings etc are saved on the machine so you don't have to re-enter this. The backup and restore feature can take a while depending on how much data you have on the drive to start with. I had 46GB and it took about 1 hour to backup and 1h45m to restore.
The only problems I had were that the screws holding the drive in place were very tight. To avoid rounding the heads off you should use a philips screwdriver that fits perfectly. The other problem I had was that when I restored the backup, I forgot to attach my external hard drive with the data and it restored the PS3 back to factory settings. There was no warning of this so I was a bit panicky! No problem though as all the data is contained in the backup.
I would recommend doing this to anyone that gets short of space from time to time as it saves time in the long run!