I've got a Fuji track pro with a 2" dent in the downtube a little above the BB welds. The bike rides fine without any noise but it looks like it's warping slightly (see pic) and I wanted to get a second opinion on whether it's safe to ride (or whether I should bring it into a mechanic for a real look )
too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Odds are it'll crack eventually, but that could be a week, month, year or decade. Of the various places a frame could crack this is about the safest, so discounting the risk of having to walk or hitchhike home, it's probably OK to ride if it still tracks well.
BTW- keep an eye on it for any hint of crack formation, and when you see the beginnings of a crack, bench it.
You could wrap it in carbon fibre if you're so inclined. No worries then when the aluminum goes. It won't look pretty though, the CF I mean. I did it with a black bike and it's like a cast on the chainstay. I'm a big fella it's seen constant service since February of this year. I used a kit from ebay that was 25$, so it would be cheap peace of mind if you're so inclined, but I agree 100% with the assessment posted above as well, FWIW.