dnomel:

Since you have thrown this open for general comment
and opinion, here is mine. All aluminum alloy frames will
eventually fail, if ridden enough to subject them to
repeated small repetitive impact stresses that lead to
stress fatigue. This is simply a fact related to the
material and its properties, and is the primary reason
why airplanes get retired at a certain mileage/age
(or sent to third world countries where we, here in
the USA, don't care as much if they kill people by crashing.)

While it is possible

it is also quite within the realm of the possible that this
crack is a warning of such a failure --certainly it is in the
right place (near the BB)--although you gotta wonder about
the dent.

In my experience, bike riders are usually more on the risk
taking side of the population. If you are like me with regard
to thrift, I understand your desire to try this frame out
since you already have it and it costs nothing. Certainly
the odds are that even if it fails, it will not be catastrophic.

I have a Fuji mountainbike that is alloy framed. Even though
I don't believe in the material as a valid approach to bicycle
frame design (components are another issue), I figured I
ought to try it out at least. It rides very nicely, climbs well,
is lightweight -- surprisingly functional overall.

I own it early in its life cycle, so I think I'm reasonably safe
on it. In your case, just make sure your health coverage
is current.

Regards,
Mike Larmer