At work I use Windows->Putty->Linux->tmux, at home I use Linux->urxvt->ssh->Linux->tmux and Linux->uxrvt->tmux. When working on a Linux machine directly, I also use a tiling window manager.

Do you mean as opposed to people who use screen, or as opposed to people who somehow do without either? Since tmux was invented in the OpenBSD world, I expect it's still mostly Unix users.

For me yes, Win7 + MobaXterm which totally rocks, so much so I paid for it. Worth the punt just for the X support i.e. PyCharm running on remote server with UI on my Win7 desktop.

No. It is very difficult to get tmux running on Windows. Not impossible, mind, but not as simple as e.g. 'brew install tmux'.

recent post on using tmux on cygwin inside a mintty https://news.ycombinator.com/item?id=6737795

Nope I use it almost exclusively in Linux.

I use a mac, and tmux essentially gives me a tiling window manager for most of my dev tasks (vim + terminals).

Nope. Linux, FreeBSD and Solaris. But mainly Linux