For the record, here are the details of my failed water pump (75,000 miles). The main bearing had developed a leak. I got the old part back just to see if I could visually detect any problems:

First, this water pump seems to be built very ruggedly. The stainless impeller blades are heavy duty and the general appearance of aluminum casting and machining is almost impressive (it ought to be for the price - see below).

Unfortunately, the shaft on my pump apparantly had shifted axially in the outboard direction, thereby causing the impeller blades to "scrape" against the housing. There is a resulting prominent groove in the housing. Now, where did all those aluminum shavings go?! (picture attached - wait for it to load)

Also note the expense required to replace the water pump. The part is about $170, plus four hours labor, antifreeze, etc., and the bill comes to over $500 quickly! Ouch!