Here's a fun bit of damage to a rim
 

Nothing too far out there (and sorry for the iphone picture), but I felt like sharing....

http://i44.tinypic.com/w7eoag.jpg

The rim is an Open Pro (though this post is absolutely not a dig on Mavic!) on a rear wheel. The dark line through the braking surface is a crack- above the crack, the rim is bulging out.

It started six months ago or so, loaded with weight on a bike tour, when my tire flatted out, and I hit a pothole. This caused the rim to bend inward very slightly right at the impact. I carefully bent the rim back into shape with a crescent wrench, but it was never like new again. The hit also put a slight flat spot in the wheel, and spoke tension has been a constant-but-manageable issue.

~3000 miles later, I've got this crack.

Luckily, I've already got the parts for my new wheelset, and a spare bike as well, so no worries :)

From the picture it seems the rim is pretty badly worn all around the brake track and the crack occured when the metal got thin enough. The earlier damage and the crescent wrench repair probably didn't help but I don't think it was the ultimate cause.

I've had two rims fail similarly from brake track wear and, fortunately, neither failure was severe enough to strand me.

I think funky grime on my rim makes them look worse than they are- my braking surfaces ARE slightly worn, but I've seen far worse (as in, big grooves all the way around).

Either way, my next build/wheelset is going to be with disc brakes (this is my commuter/tourer). Hopefully discs (and avoiding potholes) increases their longevity....

I have a very similar crack on a rim, but mine occurred when a driver swerved out in front of me during a commute and I was forced to fling myself and my bike over a 8" tall concrete curb.

Obviously time for a new bike just to be safe! Possibly some new shoes too to prevent that happening again.

Hah.

I've been wanting discs (and a matching wheelset) for a while- this just gives me a little more reason :)

I'll be lacing the hub onto a new rim, as a spare.

CXP 22 is so much stronger than Open Pro. Cost is around $29. Open Pro is best suited for racers who are obsessed with shaving milliseconds on a road course.

Looks more like an Open crack Pro rim ??
I guess the bottom line is the rim is worn out. None of them last forever and the fact that this rim might be designed more for lighteness(racing?), the MTBF will be much lower than a more robust "touring" or off-road type of rim.
Just wondering, what kind of brake pads are you using on those rims?? Could they be Modolo's "Sinterized" brake pads??, which I heard are rough on rim surfaces.

Chombi

I've been using a variety of mid/low-end Avid and Cane Creek canti brakes of them (they're on a CX/touring bike).

I;d also like to make clear, since I didn't earlier, that the crack is right at the spot that bent/that I bent back into place.