My wife does, and usually it's a LOT.
We discovered it when I was going down on her and using a dildo on her at the same time. She let go when I pulled it out and WOW! - she shot all over me!
Since then, I've done that to her a lot (we put down those pads you get for incontinent people at Wal-Mart, then throw them away when we're done), and, sometimes, it shoots out a good 18" or so. It's really HOT!
As we've discussed it, we've determined that she's been doing it for years. I can remember virtually every time we've had sex, and can recall vividly the earliest times I was fucking her with me on top and the sound would change to a "sloshy" sound. At that point, she'd be cumming all over the place. She used to think it was urine, so she resisted it, but when she figured out it was HER cum, she let's loose with it.
Probably the first time it happened was when we were 69'ing - she was getting into it really good, and started gushing into my face. I nearly drowned! Literally! I had to stop eating her pussy and turn my head so I could breathe!
Yeah, she does it, and it's HOT as everything!