Slashdot linked up this BBCnews report on new research into the "Deja Vu" effect. By hypnotising research subjects and presenting them with specific objects and suggestions, researchers claim to have dissociated the part of the brain that recognizes things as familiar from the part that perceives them. The effect was reported by many subjects as feeling very much like deja vu.
Like nearly everyone else, I have something like that happen to me on occasion, but to me it feels like I've seen something before in a dream. The feeling is strong enough that sometimes I think I should log my dreams, if only to prove to myself that's really not what's happening. However, since none of these "flashback" have been of, say, the final scoreboard of the next superbowl or the race results of the next Kentucky Derby, the need hasn't been particularly pressing.