48 hours on Twitter

I certainly learned about Twitter and I learned a little about the other members of the cohort.
My experience with Twitter took a turn I was not expecting. I signed up my seven year old son and sent out an email to his closest relatives. Currently my 75 year old mother is on Twitter following my son (only 2% of Twitter users are over 65), they are separated by 3000 miles and do not see much of each other. So we have a soon-to-be-native, and an immigrant who is sort of still in the old world. The thing that made this happen is that from both of their points of view Twitter is pretty easy to use by both independently. They have both exchanged news about themselves which was slightly banal but does reflect their day to day life.
I got to interact with my son learning to use Twitter and this was huge for me. He learned about the shift key which was prompted by the spell checker always saying he was misspelling proper names by not capitalizing them (so he learned that the first letter of proper names are capitalized). The spell checker allowed him to work his way through all but his worst misspellings without my constantly calling out spellings. The spell checker was fascinating to him, looking at the choices and getting to choose the right one because he recognized it spelled correctly. It was all fascinating for him but but not for long, he quickly absorbed the lessons he learned and used them to move into new territory.

My kids are not exposed to a lot of media. They don't watch much TV, they play a video game called Crayon Physics which requires them to draw pictures that obey all the laws of motion in order to move a ball, but no wii. We don't impose this on them (well obviously we do) but it just seems that is the way we have all evolved as a family. Don't worry they play hard. Twitter seems a great start to his "nativness": it is teaching all the lessons I want, communication, writing and spelling skills, and basic computer fluency. Are there any computer naysayers who think this is a corrupting influence?
So Twitter: cognitively appropriate for 7 and 75 year olds and gateway app for young natives?