One of the things that bugged me about Martha was how she claimed to be in love with him. My response was, "Really? Why? You've known him for like 2 days."
Actually, Martha never claimed to be in love with the Doctor until "The Family of Blood" -- episode 9 of the season, and an unknown amount of time after she met the Doctor. (We don't know how much time took place between "42" and "Human Nature.")
Was it really that many episodes into the season? I marathoned the whole thing on DVD, so maybe it just seemed a lot sooner.
Yep. As others have said, Martha had feelings for the Doctor very early on -- she was incredibly frustrated when they shared a bed in "The Shakespeare Code" yet he was not only uninterested in her but also prattling on about Rose -- but it was only in "The Family of Blood" that she described herself as being in love with him.