I've had pretty good experiences with their open source driver running on a HD 3870. No tearing, KMS support, good stability. I don't have a need for much 3D performance, nor do I use OpenCL. I just want something that runs well without crashing, and supports the new Linux 3D architecture (DRI2, KMS, DRM etc.) so it can run Wayland.
I've never really understood why you'd want to burn around 100W if you don't have much need for 3D performance and all you want is good desktop performance. Surely there are cheap alternatives at less than half the total board power?