My entire keypad has bubbled pretty badly, it makes "sticking" noises when i type, especially toward the middle of the keyboard.
My build date is 42/09, and i pretty much always use the keyboard, so it's gotten a lot of use. i think the keys were fairly flat when i got the phone (just a bit curved). some still are, Q and the right alt key are flat. enter and menu are starting to curve, and everything else is pretty much bubbled.
I don't mind the keys being bubbled, but the keyboard feels cheap to type on now, since it unsticks itself pretty quickly.
http://img257.imageshack.us/img257/2070/p1080926.jpg
YouTube - P1080927.MOV