Interesting thread, I've only just found it. My two-cents worth (not US, I'm getting ready for the euro)....

In music (tune) sessions, men still dominate by at least 4 to 1, sometimes 10 to 1. But I run a music session and my husband does the raffle, so the stereotype doesn't always hold. I also sing, so I can offer the following observations:

In "acoustic", contemporary clubs, (I'm talking of the UK here, can't speak for the US) the standard act is man-with-guitar. Women are very much outnumbered, and not taken seriously if they don't have a guitar (which most of them don't).

In traditional song clubs and singarounds where unaccompanied song is welcomed, women sing as much as men do. Women are often among the best singers - and, I have to say, the worst.

If you get a duo, it's much more likely that he plays and she sings than vice versa.

And (here's the most sexist bit...) - women are the ones who will keep the wheels running: they send e-mails, phone people up to remind them what's on, share words and tunes, make and circulate lists and calendars. Most of that stuff in our area is done by women - not women who are "servicing" male performers, but women who run things, promote things, offer lifts to gigs, perform in their own right, and make things happen. Even the mailshots etc. signed by males are often facilitated (or written) by females. The whole scene would collapse very quickly without women's contribution.