Yep, usually pretty common. My game plan has been to approach the question based on if the interview is closed or open file.
Basically, be honest about who you are. Obviously, you get the interview because they know you have the basic smarts - prove to them you aren't some science robot.
That's not a bad approach.
After finally getting to sit on the other side of the interview table and talking with classmates who are doing the same, a couple of observations I've made:
Ignoring me. For reals, though. If there is more than one interviewer in the room...or a student or an observer, don't just talk to one person. Eye contact with everyone in the room whether they asked the question or not. Admittedly, this particular interviewer is REALLY big on this. I did everything short of stand up and wave my hands around to get one guy to look at me and not just the interviewer. I assume it's just nerves and not poor form.
Nerves. I know you can't do much about it. But if it's distracting (voice fluttering like you're about to cry, nervous tics, etc)...well, I don't know what you need to do to try and overcome it.
Know when to stop talking. Maybe I have ADD or something, but I got bored a few times with long answers. I just sort of stopped listening. I guess it depends on how interesting you are, but maybe look for body language or something so you know when to wrap it up. In particular, the 'tell me about yourself/why you' question. Depending on your approach, those questions overlap. I don't suggest answering it like it's the only question you get and you need to lay everything out on the table. It was closed file, but don't cover your whole application in one question. One guy pretty much went down the list....leadership, volunteering, general academic performance, work experience. That's a little much and went on too long.
Along those same lines, answer the question and don't wander. It kind of goes with the above. Don't go way out of your way to try to bring up something in your application you just want to throw out there. Tying questions back to you and how awesome you are is nice and all, but make sure you actually answer the question asked before venturing there.