>2.)  Often times they can be brought back to life even when they 
>are clunking just by dissasembly, cleaning, greasing and putting 
>on a new boot.

This is true, but there is also another, simpler solution.  Unless 
there is a torn boot and the CV is actually out of grease, you can 
simply remove the axle shaft and reverse it, or swap left and right 
axles.  That way, the CV is no longer riding on the worn spot that 
caused the clunking noise.  The noise will often go away, and with 
luck, you could get another 100k miles out of it until, over time, 
another wear spot forms.  
This also works with busses, by the way, and (I'm told) with bugs.
-Ron Salmon