At home, always, out and about, mostly. Depends on whether I'm going to get lucky or not. If I think I am, I wear cute panties, if I'm not worried about it, none at all. I hate underwear.
I'm not a huge fan of going commando unless I'm wearing comfy pants...tight womens jeans? Not a fan of having them rub off on my bits n pieces all day long.
I really hate not wearing underwear. Partially because to me it's more economical to do one load of laundry that happens to contain 30 pairs of underwear than however many loads 14 pairs of pants and jeans might take. I can never predict when my vag decides it wants to start oozing stuff, so I'd rather not take my chances, lol
Always - It's my Master's number one rule. No panties - EVER!
It gets tricky when ya wear a shortish skirt and the day ends up being windy. But I LOVE to live dangerously...hehehe.
NEVER, Ever since I got back from Iraq I just got so use to sportts bras an boyshorts thats all I wear. Sorta weird I know. I keep telling myself Ime gonna actually wear a regular bra and thong one day, never happened yet.
I usually wear jeans and I find going commando SO UNCOMFORTABLE. It's like someone tried to stick a denim jockstrap between my labia -_-
Dusk - I would have expected most to respond as you did - very surprised to hear how many girls actually do. Most men think this is an urban myth. When I asked my wife about it she just laughed incredulously - anyone hear of vaginal discharge?!
But apparently it works for some - just not anyone I know.