bare metal will rust if not covered. If your truck is in pretty good shape over all (mine still looks brand new) I would let a pro do it.

If it's already banged up and you don't mind that your own repair may not look perfect then go for it. Bare metal may require priming for the paint to stick - haven't had to deal with a scratch that bad yet. Some searching around with google will probably yield lots of advice on doing it yourself.