My daughter is 3 and I actually first started her on a tablet as it was more intuitive and she loved it! She has since moved up to operation a computer mouse and playing learning games on pbskids.org
and nickjr websites.
I figure the world is changing to be more and more computer related so why not start her early? Heck, they don't even teach cursive writing at my nieces school anymore because everything is typed now.
Edit: Corrected my horrible typing mistakes as I'm a terrible at typing on the phone.