Just remember that doing a large number of procedures doesn't necessarily mean that they are all being done well, especially for procedures that are fairly new. A surgeon who began doing them when the technology first came out gets a "head start", so to speak, and gets referred a number of patients simply because he's the only one doing the procedure.
All procedures have learning curves for the surgeon, and the learning begins during the residency program, so almost by definition you are likely to be "on the curve" if you have it done at a teaching center (which isn't always bad), or if you have it done by someone who has only done a few of the procedures. But also, all surgeons learn differently, and some never seem to master certain techniques despite doing a fair number of them, which is obviously why this question is so hard to answer.
If there is any way you can talk to people who observe the surgeon regularly, you are most likely to get valuable information from them. This would include operating room personnel, anesthesia people and assistant surgeons.
I faced this decision myself 2 weeks ago. In fact, I elected open radical prostatectomy instead of the robotic or laparoscopic procedure based on the knowledge that my surgeon had done a "significant" number of the procedures and was known to have a high level of skill and confidence doing the procedure. I don't regret that decision. My course has been uneventful and I ended up having [b]zero[/b] incontinence since catheter removal (an outcome that is frequently linked to the technical skill of the surgeon).
I had an inside track, though. I'm a surgeon at the hospital where I had the procedure done. But I think the principle is quite valid.