So, I bought a 160 GB hard drive that I will be installing tommorow.

My question is, will installing the hard drive cause me to lose all of my trophies?

Are trophies stored on Sony's servers somehow?

If you do a back-up to an external drive and restore that to your new HDD, you keep your trophies.

EDIT: Did you get an enclosure too, Domo?

Unfortunately, the only other storage device I have is a 2 GB thumb drive, so I can't just back up my whole HDD.

I know that trophies are synchronized with the PSN network, but I know they are saved on your firmware first.

So with the hard drive upgrade, I'm thinking I might lose all of my trophies.

Erase all your media (movies, pictures, music), all demos, all PSN games, all game data (not save data) and you should be able to fit what is left on that 2GB thumbstick via a backup. It's the only way to be sure to keep your stuff.

Good idea.

If you take your PS3 online and sync up your earned trophies with your account, I don't think you'd lose them.

What else is really important to back up apart from saves?

You answered your own question. For a 20$ investment, you get utility out of a perfectly good formerly PS3 HDD. It can then be used for media or as a backup device.

lol, I like to make conversations easier by getting two birds with one stone.