Are there specific hard drives for the PS3 that I have to get or will anything do? 'Cause I wouldn't mind an upgrade.
The official upgrade page (linked farther up) made it sound like all you needed was a standard 2.5" internal Sata drive, so I got a Seagate Momentus 5400RPM 320GB (the same drive family and type as my current one, just 4 times larger). Nothing special. Some folks talk about the benefits that come with adding a 7200RPM drive or an SSD, but the regular load-times never bothered me that much (barring ridiculous exceptions like MGS4 and Lost Odyssey), and investing in a high-end 2.5" drive for what is now officially last-gen seemed really silly.
EDIT: FYI, I haven't played anything yet because I've been downloading shit. So you may want to hold off until I report back.
EDIT2: So it appears that when playing games you already had played on the old HDD, the PS3 re-writes the note that says you have played it before and treats the game as if you've played it on the machine for the first time. Mind, it won't delete anything in the "saved data utility" folder, it will re-write data in the "game data utility" folder. So it depends on how exactly that game uses save files.
Person 4 Arena (disk) - save file not recognized, re-written, starting from scratch.
The Last of Us (disk) - loads from the save file in the saved data folder, worked perfectly.
Warriors Orochi 3 (digital) - auto-loaded save file no problem, worked perfectly.
2/3, and the games that I would really want the save files to work are the ones that work. So there you go.