Mine have a slight up and down rocking motion. But they don't feel loose or cheap enough to fall out of the phone, not yet at least.
I thought the physical buttons would be a plus, coming from the Eris that had HORRIBLE capacitive touch buttons. I tried the Inc's buttons in the store, and they were a dream compared to the Eris. I chose the X over the Inc, and yes, the physical buttons are probably my biggest pet peav about the phone. But not big enough to make me drop the X.
I consider them a small minus in a vast sea of pluses.