It's difficult to get a sense of real world "weight" with CG - want to see some enlightening miniature work? Check out the extras on the LOTR trilogy! They actually refer to them as "Bigatures" because they're quite large!

James Cameron is also a fan of using oversized miniatures - for True Lies the bridge they blew up was a good 6 feet tall above the water - it makes the waves look more normal. A teeny miniature over water is quickly dismissed as a miniature - water doesn;t shrink, and the only thing you are able to do is blow air across it to hopefully create smaller ripples, but it usually just looks like you're blowing air over water.
CG and matte painting are fantastic, however, for set extensions and background elements - better done that way than with miniatures.

What are you shooting? Or were you just wondering?
-Lew ;-)