<p>Ok, I guess a little clarification is needed on what I'm saying as I skipped some information. Firstly in my own experience "door knocking" was the key to things but not in the usual way: I sat in the majority of professors' offices before I was even a second semester sophomore because I love to talk about physics. (It was around this time that I made the discovery that asking ten different physicists the same question means you get ten different answers...)
So anyway, come job search time I sent off emails/ went door knocking, and it came down to the professor who enthusiastically wanted me to work for him and the one who kept telling me to send me an email as he wasn't sure yet, even when I asked him if he'd made decisions after class. I guess what I'm saying is when you want to work for someone you ought to take hints for precursors to come, and I didn't like the signals of that prof.
Of course, it is worth noting that due to university budget crunches hereabouts, I am the only rising junior on the physics dept payroll, and I'm sure it's because everybody knew who I was even before I went around asking as it's not like my transcript is particularly stellar and such. So it never hurts to go around to say hello to people, even if it's just to talk! :)</p>