I have a boat and I dive solo all the time. Now I always have someone topside with laminated instructions on how to operate the boat, use the VHF, what to say to the CG, etc., etc., etc. I also train my friends on these procedures.
Up until last year I would sometimes dive (with a buddy) with no one on the boat. In retrospect - that was a really bad decision. I dive miles from shore and if the boat were gone - we would be really screwed. Once we surfaced, got into the boat, and started tearing down our gear. Usual chatting about the dive, etc. I look up after about 5 minutes and we had drifted 50 yards! The anchor had lost it's set and we started drifting in the wind. When I would do this I would descend down the anchor or mooring line to make sure everything was in good condition and the anchor was set well. As we all know conditions can change and they do. Lesson learned - it is MUCH safer in my opinion to dive solo than it is to dive with a buddy with no one on the boat.
I enjoy solo diving sometimes as well. Yesterday I was out with 3 buddies on the Crane for a short deco profile. They wanted a longer bottom time than I did so it made sense for the two of them to buddy up and I went solo. While I dove they were topside and vice versa. It was really dark, the vis was terrible, and it was still freakin cold - 43 degrees at 142'. My plan was for 15 min of bottom time on air then deco on 67%. It was so cold and ridiculously dark that I opted for the 10 min short plan I always include on my deco slates. With my 67% EAN I only had short stops at 30' and 20'. Anyway....come to think of it....7 of my last 8 dives have been solo. 2 solo deco dives on the U853, 2 solo deco dives on the Crane, 2 non-deco dives at Burnham, and 1 non-deco at Paddock. I also enjoy diving with buddies but it many cases if I don't dive solo I don't get to dive.
--Matt