I believe your brain stores information and your mind replays in dreams but I also believe that dreams can tell you something about the future...or even the past...I've heard of people having dreams about possible past lives...
I'm not crazy..I'm just interested in weird stuff...haha
It only seems like your dreams replay the day because that is the easiest information for your brain to use to reconcile the various neuron firings.
Myself, I rarely have dreams like that... at least, not ones that I remember.
Which is another thing - once you're awake, if you try to remember the details of a dream (especially after a half hour or so) your brain will tweak the dream so it makes sense.
On the subject of clarivoyent dreams: I think it's BS. I've experienced deja vu myself from a dream in the past, but only because it was vauge and fit a whole range of possiblities.
@Sephiroth: Your brain does the sorting out of information as it comes in. You still remember being yelled at the next day, correct? Yet, ten minutes after you pass a car on the road, you can't remember it's licence number (unless you decided it was important) even though you saw it. Memory is not 'thrown away' in your dreams. REM sleep does assist in moving important information into long-term memory, but that's not it's true function. (REM's true use is to eliminate fatigue toxins from the bloodstream and rest the concious mind)
Wow... long post.