We're all over the shy/outgoing and introvert/extrovert map in our family. I am definitely an introvert and was very shy until I had kids (and I still don't like certain situations where I feel on-the-spot; I used to whisper correct answers to my friends in high school so that I wouldn't have to raise my hand and speak!). DH is not shy but does tend to be more introverted. DS11 is extremely shy and introverted and I can't see age changing that a ton -- although with growing up I hope he does gain some confidence (which, to me, is a different issue). DD8 used to be shy, but this year with the grade acceleration is no longer shy and is showing herself to be quite extroverted. I think, in her case, keeping her with agemates contributed to her shyness since she was trying so hard to fit in that she couldn't show who she truly was. And DS6 has always been both extroverted and outgoing, both before his grade acceleration and after.
So, in answer to your question, I don't think it was a mistake to consider grade skipping. I think that it can work for any personality type. It's success depends on the kid and any number of factors, but I've personally seen it work well for a shy kid. (Although I do remember that DD's 1st grade teacher knew she was advanced but never thought to do anything about it since DD was so quiet and never caused any problems; I also remember the receiving third grade teacher at the beginning of her subject accelerations being worried that the accelerations wouldn't work because DD was so shy.)
In general, though, I agree that it can be much harder to know what is in the brain of a gifted shy introvert than a gifted outgoing extrovert. My DD8 is probably a higher LOG than my DS6, but the difference is that DD8 often suprises us with what she knows because she keeps most of her thought processes to herself, but DS6 talks non-stop about everything going on in his little head!
