I hear ya mannnn. But don't go back to film. Oh yes, I still shoot film - very occasionally though - but mostly slide film when someone asks for it. But beyond that, high resolution digital photos just blow film shots out of the water. I know that the D100 can frustrate you - especially if you have a unit that does the underexposure thing - but if you learn to work around it, well, then you will become the better for it. Of course, what makes it worse is, if you know someone who has a D100 and it is exposing perfectly right out of the camera with all automatic settings - which lends credence to the unit-to-unit reliability issue.
Here's something else I forgot to mention in my earlier thread. I also purchased a Fuji Finepix 602 Zoom which is 3.1 MP with 6 MP interpolated. That camera also takes exposures that are superly balanced in most scenarios - althought the overall resolution cannot match the D100. I bought that for point and shoot purposes, and yet I find myself often taking it along for the ride quite a bit. Go figure!
So hang in there, and if things don't get better for you, by all means try and sell the D100 - you should get top dollar for it, and then try something else.
I hope - no, make that I really believe - that Nikon has got to come out with a firmware upgrade to address things like underexposure, the DTTL flash scenario, and of course JPG sharpness issues. If they don't...well, then there will be folks who may just leave the flock as they migrate to competing brands who have managed to work out the problems that Nikon seems to be ignoring.