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.

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