I've been paying very close attention to the symptoms over the past few days of driving, and it's very consistent. Basically, first thing in the morning, car is cold, the clutch is PERFECT.

As I drive it and it warms up, my clutch pedal engagement point lowers to the point where it engages right off the floor (as opposed to approx. 2 inches off the floor when I started).

So I think it's only one of two things:
1) Faulty master cylinder
2) Clutch fluid has absorbed water which is lowering the boiling point of the fluid, causing it to perform poorly as it heats up

Anyone think I might be on the right track here? I am going to get some new DOT4 fluid and flush the entire system. If that does nothing, then I think I'll need a new master.