+1 on that budyy. I have a thermometer on my boil kettle, and for the life me, I don't know why. I never use it.
I wonder if this is a function of the type of chiller and\or kettle used? With a standard kettle, your average probe-style brewing thermometer has the bracket for mounting on the lip of the kettle - this is rendered useless on a converted keg whose opening doesn't have a vertically-oriented mounting point. Also, if you have a therminator or other chiller that shows the temperature of wort exiting the kettle, I can see not needing a kettle mounted one, but with an immersion chiller, it's sure nice to quickly glance at that big dial, without having to find your probe, sanitize, insert, and wait for a reading while running through your end-of-brew process.
Having a keggle, I personally can't wait to install a thermometer