I use it. I use 6 and 5, been staying away from 7 because of SoftWrap.
Also, recently I found out about
Enigma, which is just like GM [it's main file format is .GM6 even], but it's free [but currently broken in strange ways, notably collision and currently only supporting the code DnD block].
I'm working on a project in GM6, bilateral, but my current machine is a Vista box, so...