Yeah I think Goalie's advice is generally true but maybe not so much when you're dealing with branch offices with only a few practice areas? I wouldn't necessarily characterize Wilmer Boston that way but I have another Boston interview tomorrow where the office only has 3 practice areas, one of which is IP. I had to call a friend I know who works in that area to tell me something about it so I could be like, yes, I am interested in such and such and I'm not just some moron applying to your firm because it looks pretty.
Fair enough. I do think it's good enough to just know that there limited practice areas, and make sure not to mention a strong interest in something that they don't do. Of course, as Stan mentions, if you are HONESTLY really interested in IP or something, it's good to mention that. And showing that you've at least looked at what practice areas they have is a good idea (but again, not crucial, I don't think). I think it's honestly fine to say "I know your Boston office is strong in securities practice. I'm sure I won't know whether that's something I want to focus on until I try it, as we all know law school doesn't teach you anything about the real
practice of law, but I'm really looking forward to learning more about it this summer." (BIG SMILE).