I am a recent C70 owner, having had the car for only a month and a half. But there have been zero issues (knock on wood) with my car. In my pre-purchase scanning of various forums, it seemed to me that most of the C70 issues fell into the category of early "teething" problems, that mostly impacted the earlier-production 2006's. As far as I can tell, these issues have been corrected by Volvo in current production, and were addressable in the earlier cars via dealer-provided updates, etc. (Things like software/firmware bugs in the car's electronic controls, an issue with cables in the top mechanism rattling a bit, and other relatively minor annoyance-type issues.)

My big pre-purchase concern was with the basic reliability of the top mechanism. Other than minor adjustment issues, I found little evidence of people having problems with the top mechanism. My own top was apparently adjusted well from the get-go, as there have been zero issues with it.

In buying a 2007, I felt that I was avoiding any early design problems. I had confidence in the basic mechanicals, since the platform is from the S40 (albeit beefed up for better rigidity without a fixed roof), and the engine and transmissions have both been around a while.

I'm totally satisfied with the purchase, so far, although admittedly it is really too soon to tell about reliability.

As an aside, the other cars on my short-list were the Audi A4 2.0T cabriolet, and the VW EOS (also the 2.0T version). My wife and I liked both of these competitors a lot, but we REALLY liked the C70 (even though both the Audi and the VW had some specific advantages over the C70 in some aspects).