UV Filter or No?

So between your camera body and lens you find yourself toting around some pretty expensive toys.  Is there a UV filter on the front of that pretty expensive lens?  If so, how much thought did you put into it's selection before buying it and putting it between you and your pictures?

This is a conversation in which I was recently involved and thought it interesting enough to document here.  If you don't have a UV filter protecting your lens glass... WAKE UP!  I've read about it/heard about it enough times that I'm content with learning from those other people's experiences.  Someone knocks the camera off the coffee table, drops the camera bag when taking it out of the trunk, bumps into the wall with the camera slung over the shoulder... and then comes that cracking sound!  In nearly all the versions of this story that I've heard, the cracking was the sound of the UV filter breaking and NOT the lens.  What would have happened without the UV in place?  The real question is, "Can you afford to find out?".

Assuming your now sold or have already been sold on the deal, the next question is "How much do I spend?".  While I'd argue that whether you spend $20 or $120, something is better than nothing, I'd also ask why you'd be inclined to spend $$$ on that nice new lens and then put an inferior piece of glass in front of it to save yourself what amounts to pennies when compared to the cost of the lens?

When I finally purchased my Nikon 18-200, I screwed on a B+W XS-PRO and haven't taken it off since.  If I do get a scratch in it (which will be difficult if you use the lens hood too), I can simply unscrew it and put on a new one.  The lens is protected.