In my humble opinion, De Ja Vu is like psychic ability, as you know, not everyone has full psychic ability, I believe that de ja vu is a little piece of psychic ability that gets opened up every now and again..
Again, in my opinion, I beleive that everyone is born with the capabiltiy to have psychic experiences, however it does not develop in everyone for any number of reasons, either it just doesn't or life experience and/or personal beliefs can dull and mask the sense.
I don't know.. I often have de ja vu and dreams of events that go on to happen, however i would not class myself as being fully blown psychic...
As I said, these are just my opinions. It's certainly how I explain it to myself when it happens...
It will be interesting to watch this thread and see what other people think too.