Numerous studies have shown detrimental effects to child brain development associated with the early introduction of television and computers. No, you can't get around these detrimental effects by using "age-appropriate" or "educational" shows and games. Apparently, something about the *medium*, not simply the message, is causing these negative impacts. Perhaps it's the pacing of the material, the quick transitions, or the sugary over-the-top positive feedback that they get for completing even the most simple task in an educational game. For me, I don't need to know exactly what is causing the negative impacts - I see no serious side effects associated with withholding computers and television for now.
I know you might thing that you're helping your child out by letting him get an early start on computers, but keep in mind that some things are much easier for someone to learn at a particular age. For example, I always have to bite my tongue when one of my friends tells me with great pride "It's AMAZING! My two year old already knows how to use a mouse!!!" I always *want* to say "Were you really under the impression that he was going to have a problem picking that up?" Honestly, people, it's a MOUSE. It's DESIGNED to be easy to use. I think it would take a 10, 20, or 30 year old with no training about a minute to figure it out and an hour to master it, and they'll understand the full context and purpose of the mouse and the computer - things that the 2 year old couldn't possibly comprehend. Controlling a mouse isn't something that your child needs a "head start" on.
You could attempt to teach your 2 year old the periodic table, but I think we can all agree that he'll pick that up just fine when it's time to study Chemistry in high school. Maybe it's time to focus on how to dig holes, stack blocks, and chase you around the house instead?
"Though a program be but three lines long, someday it will have to be maintained." -- The Tao of Programming