I've been on T for a little under 4 months, and I've definitely noticed emotional changes. Not so much mental changes. I was always good at spatial concepts, and always physically awkward. Both are still true. My language skills don't seem to be affected either. My social skills seem to be improving, but I think that's more because of the fact that I am so much calmer and happier than I was before.
There is only one mental change that I have noticed so far. It's hard to explain, but there have been subtle changes in the way I perceive sex, intimacy, and relationships. It's as if there is a greater separation between the concepts than there once was. I now understand why guys will have affairs and then say, "It was just sex." It's not only to do with the greater libido, there's something of a different mental perception as well.
I'm also finding that women are becoming even more alien to me than they ever were, but that could just be because I'm focused on becoming "one of the guys" at the moment.