As you and I seem to be pretty close in age I thought I'd comment on my situation and also recommend you read my blog as it does for into detail about
"mr happy" and his ups and downs.
I too had Da Vinci surgrey, and it went very well. Indeed I too was getting the odd sensations even within a few hours after the operation. The one thing that really put me off was the thought that an erection would damage the catheter while it was still in me.
After a few weeks i was getting some pretty good erections, even to the point where intercourse was possible. Now things are still very good. I can maintain a decent erection when in the "mood" but unfortunatly because I am such a sensitive person the emotional side effects of PC does sometimes mean mr happy goes back to sleep at the most inconvenient times.
I spoke to my consultant a couple of days ago and explained this and he said that because PC is basically a massive emotional rollercoaster I would experience times when I would not be able to perform as I used to. I then explained that I had tried viagra and that the 1st time was amazing, but the second time it had no effect at all. He suggested that perhaps that was more to do with the presure to perform rather than the effects of PC.
Also, and here is a very strange thing. You may notice that you produce a very small amount of clear liquid during an erection. When I first saw it I was shocked. Basically, and I couldn't comment on anyone elses situation, my cowper glands have been left intact and they produce this liquid. Have a quick google for cowper glands and that will explain all.
Anyway, good luck with the recovery