It would seem that this is a double ended question when coming from the interviewer. I have conducted many interviews and hired many wonderful people. The best response to the "what are your strengths and weaknesses" question would have to be that your strength is also your weakness. Cliche' as it may seem, it is actually true. In most instances, what makes a person the strongest is usually what can also make them the weakest.
i.e.; communication is both my strength and my weakness. I can have very high quality interactions with many different poeple in a very professional manner. I am able to extract the bits and peices that are useful and I am able to add to most topics brought to the table.
However, communication is also my weakness in that when the conversation turns intimate and I am to share my information, I may well find myself mute.
Above all things when in an interview, never lie. Always do the right thing and the outcome will turn out as it will.
Bset of luck,