Bicycle Mechanics - Rim showing stress marks

So a few days ago I heard a loud pop on my ride and after inspecting the bike I assumed that it was just a really unclean shift since I was going up hill. When I got home I noticed that I had in fact broken a spoke (it was still wedged in there and wasn't flopping around). I was getting ready to replace the spoke and I wiped down the rim and I've noticed small little stress marks going all the way around the rim perpendicular to the edges.

My question is at what point should I be concerned? Does this sound like it's unsafe to ride? I'll put up some pictures soon.

It's very rare for wheels to fail catastrophically while JRA, so I wouldn't be too worried. But some pics would help.

My Astral Velocity rims showed signs of wear about the spoke holes that went undetected because I didn't check my bike as frequently as I should. I did not have a catastrophic incident as a Result. I suspect I could have. But, I was atop a steep hill climb , when a spoke pulled through the spoke hole and a large crack about the opening. I called it quits and my wife came to my rescue when I decided to not ride home. It was such a large crack and the wheel so out of true, I decided it unwise to ride home.

If you mean the rim's brake surface has a stress mark, your rims are probably almost used-up. When the rim finally lets go, yeah, it'll be catastrophic. Instant tire blowout, missing brake surface... that'll do to go on with ;) Pics?

Sounds like Free's rims are almost toast..
What I"d like is a good indicator as to how far along is rim wear.. .. I see some etched grooves digging into my road bike's rims running parallel to the rim's edges - but they are not very deep. So it appears.

So a few days ago I heard a loud pop on my ride and after inspecting the bike I assumed that it was just a really unclean shift since I was going up hill. When I got home I noticed that I had in fact broken a spoke (it was still wedged in there and wasn't flopping around). I was getting ready to replace the spoke and I wiped down the rim and I've noticed small little stress marks going all the way around the rim perpendicular to the edges.

My question is at what point should I be concerned? Does this sound like it's unsafe to ride? I'll put up some pictures soon.

Some sort of Mavic rim i'm guessing? Or Velocity?