Its actually so easy, its well worth doing as the standard HD fills up too quickly.
The only thing you need to save is your game save data, and anything such as photos or videos etc, as all your settings carry over.
All game data has to be reinstalled from the original discs, and downloaded content can be re-downloaded for free.
Just keep your original drive safe so it can be refitted if the PS3 needs fixing/replacing under warranty.
Swapping the drives does not void warranty as there are no seals to break, but obviously you will wanna keep your new drive to fit to the one that comes back.
