I think it depends on the game and what he may be avoiding while getting lost in them.  I am very set against any games with violence and have a zero tolerance for them.  There are toooooo many studies that suggest a link between these games and aggressive behavior.  Games that require concentration, skill and patience can be a wonderful exercise for your child.  My only other concern is using computer time to avoid social interactions, and for this reason would monitor the amount of time spent gaming. 

As far as being on-line and surfing the net, unless there is research being done for school I don't think anything good can come of it!

Hope this is helpful!