I started out with msotly surplus, cause it was cheap and durable.
It's also (mostly) a royal PITA. Aside from the weight issues mentioned, most of it doesn't seem to be as user-friendly as the civvie stuff. Lugging an ALICE pack is torture compared to some of the newer, better packs out now.
Final disadvantage (a big one to me) is that you're automatically tagged as some kinda "paranoid survalist milita SEEL-RANGER wannabe" if you've got mostly army gear. I don't like drawing that kind of attention, personally.
That said, one advantage of the army stuff is it doesn't scream HERE I AM! in day-glo colors like a lot of the modern civvie stuff is. Being a chick who sometimes takes off by herself into the boonies, I like the option of being discreet, and not broadcasting my presence to everyone on the neighboring hillsides. Hence looking for civvie stuff in ummm... "sage," "loden," or whatever else the yuppies like to call Olive Drab these days.
Final analysis.. go with good civvie gear (army surplus is definately better than BAD civvie gear!). If you don't, you'll likely be replacing most of the surplus stuff in a couple years anyway. The exception is the USGI canteen/cup/trioxane stove setup. That thing rocks!
-K
PS -- if you still want to go the surplus route --
cheaperthandirt.com
is a good place to start.
PPS -- also check the hunting stores around you. Often just as good stuff as the REI type places, but often better prices and better suited to discretion. IE -- more subdued colors, or even camo if that's your thing. (remember RealTree and the like mudge altogether with distance, good ol' USGI is still a very recommended camo if you go that route). Also, less expresso-and-gourmet-in-the-woods-yuppyness, which I find a Good Thing.
have fun!