Boys and Their Games

I do believe the boys are addicted to the Nintendo DS.  We only have one, the one I bought after I learned my lesson on making bets.  If one of them  is playing the DS the other sits and watches.  I really don't get it. That screen is so small.  But they do it, see-

So, how much "screen" time is appropriate now a days?  Honestly, between the computer, the tv, the ds, and the xbox 360, these two would sit in front of a screen all day long if I let them. I usually give them about an hour or so after school and then tell them  its time to go play, which they do.  Then I'll let them watch a little bit of TV before bed if they want. I think it is reasonable.  They, of course, always want more time.