I have 2 Quarqs- a S975 and a Riken. Both have been pretty solid over the years of abuse, although I did have to bend up the battery contacts on the S975 a few years back. Other than that, no complaints. The S975 has been fully submerged a few times, used in the rain countless times, and generally knocked around. It still reads within a couple watts (rough comparison) of the RIKEN. So, I guess I've been lucky, and I'm hesitant to send it in lest I get upgraded and end up with a lemon. So far I have no reason to.
I also have a Stages, which I'm less thrilled with. I still need to install in on the Quarq and do a DC Rainmaker-esque comparison with 2 computers to see the difference so I can use it more effectively. Right now I was only using it on the rain bike and the 'cross bike, but I'd like to use it on my TT bike so I don't have to swap cranks around as much for stage races.
I'd love a SRM, but there really aren't any floating around here. There really isn't a used market for power meters at all, and until my Quarqs start giving me issues I can't justify one.