This is an interesting subject. (BTW MmeRouge, I missed your thread about it, but we like your clit hood piercing.)
When my wife and I started having sex she didn't come. She said she'd never been able or orgasm during intercourse. She could orgasm ok by masturbating, but intercourse didn't provide enough stimulation. I noticed that her clit had adhesions with it's hood and we thought a vertical hood ring might help. It didn't take the ring long to break the adhesions and not long after it settled down she came during sex, which was wonderful for both of us. We'll never know if it was a placebo affect, in that it worked because she thought it would, but it doesn't matter, because after that she was always able to come during sex; even long after she'd removed the ring (she took it out before she gave birth to our son in '92). But as some of you read in my earlier posts, she has been through many treatments for breast cancer and sex has been very much sidelined for us. However, we've recently had a go at getting our sex life back on the road, and she can't come. Not even when she tries to masturbate. She says she hasn't come for many months, or possibly a couple of years, and gets bored or sore if she tries too hard. I had a look and her clit is once again adherent to it's hood. I'd guess 1/2 to 2/3 of the surface of her glans is stuck. She doesn't fancy having it pierced again, so we've just ordered a clit enlargement vacuum cylinder (size small) in the hope that regular use will pull the clit out from under the hood and break the adhesions.