THC inhibts REM sleep, meaning if you have THC running through your blood stream when you go to bed (as most of the peeps on here seem to have), you won't dream until much later in the night, usually early morning. If you cut back for a day or two, you will notice a distinct increase in the frequency, vividness and bizzarness (I don't think that's a word) of your dreams.

Just remember that next time you smoke a bowl before bed.