Speaking of less common carry methods, when I was first going to carry, I was very interested in Small Of Back carry, but it is difficult enough to draw while seated from 4 o'clock and I know that SOB would be even more impossible and not at all comfortable while driving sitting all day. Many talked about hurting your spine/tail bone if you were to fall over backwards and land on the rig if it is in your small of back, but I didn't think that the small chances of that happening really discouraged me from carrying there nearly as much as the other reasons. I did see a guy at a match this weekend using an OWB SOB rig though. I forgot to watch him draw though.
As far as ankle, I can't even comfortably carry a knife on my ankle, and my ankles are too small to fit a gun.
Shoulder is elaborate (and expensive) and I don't wear a suit jacket enough (ever) to cover one. Also, you have to sweep the whole room when drawing, as opposed to just pulling from your hip. I don't think that sweeping is a big deal, but it is a pretty big and noticeable movement to reach across your body, fumble with your shirt, etc. Not to mention it only takes someone putting their hand on the back of your elbow to effectively screw up your draw.
Just my opinions on all of this though. I haven't carried any way but at 4 o'clock.