And in an attempt to actually add to the discussion -- it doesn't bother me when interviewees are nervous. Nervousness fades in a few weeks, and at least for me it doesn't really hurt your chances. Salesmen are supposed to be confident in interviews, but I don't see why developers should be. What I'm looking for is that magical combination of "this person is competent" and "I can trust this person to do a good job." I also appreciate someone who can tell me honestly that they don't know the answer to something. Anyone new to my (very small) field is going to have gaps in their knowledge, so I need to be sure that when they're unsure, I'm going to hear about it.
Prepared answers only really bother me if they have *nothing to do with the question*.