In my interview I took off my jacket because the room was very warm. I also felt that it put me on a better level of dress with my first interviewer. I think it is really about being comfortable. If it makes you feel akward to remove the jacket, then leave it on. The other interviewees I was with told me that they left theirs on. I was accepted and expect the other people to be accepted as well. One of them was bright red though... ...He just hoped that they knew he was hot and not so nervous as to make him turn red.
i would just keep it on regardless of what the interviewer is doing (unless you are getting really hot). the jacket makes you look very professional...