FWIW, I did my open water dives (7), plus about five more dives (drysuit and nitrox certs and one recreational dive) for a grand total of 12 before going to the Drager Dolphin. As long as you're someone who is capable of thinking for him/herself, I don't think there's any big deal. On the other hand, I'm a believer that there are a lot of people who should _not_ dive a rebreather...
I had about 100 dives total, all cold water/drysuit, and twelve months of diving under my belt, when I transitioned to a CCR. It was easy on the theory, but like starting over on the skills. The Dolphin helped immensely, though.
I've got a grand total of 14 open circuit dives in my log - at a few times in the interim, I did a single O/C dive and I hated every minute of it...the up-and-down of the breathing made it hard to take photos, the bubble noise was loud and obnoxious, and none of the marine life would come anywhere near as close to me as when I dove the rebreather. 45 - 60 mintues per dive in the water just wasn't long enough, either.
For me, there's no going back...
-C