Cybersex
I turn it off because I don’t like people contacting me that way. It’s a public board, I don’t feel any desire to hold private conversations. It’s not just here, I tend to turn of PM/IM systems anywhere I sign up if possible.
I’ve received two PMs in all my years here, and both had to do with a baking thread over in Cafe Society that I’d missed but people evidently remembered what I do for a living 
Other than that – I really don’t like to IM. I went through a period where I spent hours IM’ing to the extent that other more important things fell by the wayside. I’ll IM if I have something urgent to say, but that’s it. Otherwise I’m quite happy emailing.
When we were doing Finish the ___ Story threads years ago, some PMs were used at first. We decided a control thread was a better idea, since others could join in the fun that way.
I don’t have PM blocked, but I don’t use it much now at all.
On a positive note, my wife and I enjoy orgasms!
I’ve received only 1 pm since I joined, when tubadiva asked me to change my username. I really expected many more, e.g., “you’re embarassing yourself” or “I think you should stick to reddit you tool.”