This post about PvPing as a Guardian really opened my eyes. The main point is: you're a tank in PvE *and* PvP (crazy, eh?).
I still totally expect to have my ass handed to me in most 1v1 situations as damage reduction with taunts only occurs against players other than the Guardian, but even so just changing my perspective on my role in PvP has made me feel better about the whole thing in general.
The post is pretty superfluous is the point. Guard the healer so the dps can kill the other side and not die themselves, read your skill descriptions and win.