He hasn't been overused - he was only really in two movies last year (Surf's Up doesn't count). And the year before that he was in two movies that nobody ever saw. Before Disturbia, he hadn't been in a major film since Constantine three years ago. If you want to say he's a little oversaturated, with the likes of Steven Spielberg and all of Dreamworks touting him as the next big thing, then yes, you're probably right.
But baytor's right. The kid isn't making it just because he's getting media buzz, it's because he genuinely has the talent and charisma to carry films - something that's very rare for his age. People may have bought tickets to see fighting robots, but it was Shia who made the rest of the overly long Transformers watchable. He'll be perfect for Yorick.