I know what you mean about the amount of time it took for more somewhat complex life to develop. I have to keep reminding myself about geologic time, and how "slow" it is from the human perspective. It's even worse in today's have it now society.

Back to the issue at hand...what about all of the changes the young Earth was going through, i.e. volcanism (the #1 gas emitted by volcano's is water vapor), atmospheric changes (oceanic scrubbing of the atmosphere), plate tectonics, etc. My points is, the reasons for the delay are likely quite complex and the result of a combination of "growing pains."

On a philosophical note, perhaps it wasn't our destiny to evolve faster, and things unfolded exactly as they should have. For all the good my scientific mind does, I still believe in a certain amount of destiny. :-)