Yes, please let us know what the vet says.
This may sound ridiculous...but is it possible that Kitty ISN'T pregnant? I have read about false-pregnancies, and how cats can exhibit all of the symptoms (weight gain, eating more, etc.) of a real pregnancy, and then actually not be pregnant. Apparently this happens...I don't know, I'm just brainstorming.
Or, her due date was WAYYYYY off.
Or, there's something wrong...I do think the vet thing is a good idea. If for some reason she's ready to have the kittens, but isn't delivering them...I would start to worry.
I'm not trying to discourage you!!! Just keep us posted on what the vet says.