No, you're not the only one. My second key fell off of my 7100t yesterday. I believe RIM is aware of the problem, and that's why subsequent generations (such as 7100g) have a corrected key design. The problem is that now I'm stuck with T-Mobile for the term of a contract, and this is the only 7100 model they have. I've always handled the phone carefully. The problem is that the keys are not perfectly flush with each other, and their edges are not rounded, so they catch on clothes, and then easily fall off. They cannot be put back on - I've tried epoxy glue and plastic hot-glue. It's simply a wasted $200, and now I'm going to have to go to a full-qwerty unit, for another $200 - $300. VERY irritating.
Live and learn: never buy the first generation of a new product!