It depends how it's used. If it's used in a way to describe someone who is really passionate about something (as most of us on this site use it) then it's a good thing. But sometimes people use it to describe someone who is so irrationally obsessed with something they've lost all trace of any hint of ability to interact socially (think WoW/Everquest/insert addictive MMO title here gamers who play 24/7, are fat, old and ugly and live with their mom not because they like their mothers but because they don't want to get offline to support themselves) then I don't like it.
Nerds are similar only they are less passionate/obsessed with something as they know every single little unimportant fact about said topic. People can be both.