I have to agree with those chiming in that Tieflings recieving a racial penalty to Charisma doesn't make sense. Look at the more powerful fiends in the Monster Manual. The vast majority of fiends have a very high Charisma, so unless all Tieflings have Dretch blood, Tieflings should, if anything, recieve a bonus to Charisma.
I think it would fit them better, as well, since I can easily envision a master Tiefling Sorcerer. When I think of Tieflings, I don't think of shy, uncommunicative and socially inept people, I think of wily, charming diplomats, thieves, or even Bards. If I was to redesign the Tiefling, I'd drop the Charisma penalty and give Tieflings a racial bonus to Charisma instead of Intelligence.
I've never thought of Tieflings as particularly brilliant or bookish, although if one wanted to keep some kind of penalty, you could drop the Charisma penalty and give a penalty to Wisdom, which, in my opinion, is the only statistic it would make sense to give Tieflings a penalty in. Regardless, the Charisma penalty doesn't fit at all, and if I ever run a campaign with Tieflings allowed, I would definitely get rid of it.