An interesting study recently found that active video games, such as those on the Nintendo Wii console, are not as physically stimulating as they appear. This study, put on over a longer-term period, found that players were apt to complete required actions with as little movement and energy as possible, providing limited physical returns. Active video games are not the same as the real thing - just another arguement to get outside and play!
Check out the article here.
If you're interested in the full study, you can download the .pdf here.