To remind the forgetful and nuns, a male condom (aka rubber, johnny, prophylactic) is a sleeve of latex or similar rubbery substance that slides over the penis for use as a contraceptive during sex; it forms a barrier between the penis and the vagina stopping sperm and germs getting from one person to the other. A lot of work has gone into making the male condom fit snugly and make people forget they're using one.
In contrast, a female condom (sometimes known as a vaginal pouch) is a bag of thin polyurethane that is stuffed into the vagina. It doesn't fit tightly to the vaginal walls, although a ring is located at the foot of the bag and another at the opening to stop it collapsing (slipping the ring onto a girl's finger will probably not get a laugh). The condom is typically lubricated; however it will in normal use prevent the vaginal juices from lubricating the penis, so a large amount of appropriate water-based slippery stuff will be required. Another problem is that care must be taken when inserting the penis to ensure it goes into the pouch, not around the side. And even the makers admit that "the female condom can also be noisy".
The main claimed advantage of female condoms is that they are "woman-controlled" (according to the makers of Reality brand), meaning that they let women be in control of their contraception. However, you may think could just as easily carry conventional condoms with her, which have the advantage of being smaller, cheaper and more widely available. Being "woman-controlled" means it is in theory easier for a woman to insert a female condom than to get a condom onto a man who really doesn't want to wear one; however I would consider this a poor advantage in most relationships.
Both sorts of condom offer protection against HIV and other sexually transmitted infections, as well as against pregnancy. The female condom is less prone to breakage, and may offer increased sensation. Also they can be inserted before the penis is erect, unlike conventional condoms, so they may allow a little forward preparation if the woman doesn't mind more than the usual flappiness at the front. Manufacturers claim this may be done up to eight hours before intercourse; you can even push the outer ring aside to urinate while wearing it.
The brand names are Reality in the USA and Femidom in the UK. They advise that you should not use one in conjunction with a male condom. I would be worried that it would squeak, but there is a more serious risk of the male condom getting pulled off by friction. Female condoms were first introduced in 1992, and ten years later 18 million have been sold. This may seem a lot until you consider how many times people have had sex in the past 10 years.
In summary, the female condom does have some advantages over its male rival; however it has obstacles to overcome if it is to be more widely used. Not least of which is the smirking tone in this write-up. I also eagerly await the arrival of the world's first novelty female condom.
References:
http://www.femalehealth.com/
http://www.avert.org/femcond.htm
http://wso.williams.edu/orgs/peerh/sex/safesex/femcon.html
http://www.nau.edu/~fronske/fcondom.html
http://www.femalehealth.com/yourquests.html
http://www.fhi.org/en/fp/fpfaq/fpfaqs/fpfaq22.html
If anyone's offended, I'm really really sorry. I know I'm a guy (although my female friends tell me I'm an honorary girl and my male friends probably feel the same), and I also know I've never used one, but this was just such a gaping hole in E2, I just had to fill it with a little plastic carrier bag. Sorry, but if anyone does want to try it with me contribute personal experiences, feel free, and I'll try not to blush.