Lol.. I've heard about Wilbur's supposed half-hour, white knuckle, ride of your life orgasms.. no idea if it's exclusive to males or what.
As far as I have heard, humans are generally socially monogamous and sexually polygamous, with a tendency toward serial monogamy. We tend to have a series of close, long-lasting relationships, which apparently average around 2-4 years each. This has been used as an explanation of the infamous "seven year itch"... which was apparently entirely too optimistic :

:
(anthropologists suppose that 2-4 year period is the minimum length of time to get a youngster up on his feet and able to survive without constant intensive care)
Oxytocin plays an important role in pair bonding, just as Monster said, but is not alone in its role as biochemical matchmaker. The analogous secretion in the male brain is Vasopressin, which has similar effects in relation to pair bonding. In pair bonding species, the easily conditioned, dopaminergic areas of the brain (nucleus accumbens) will have vasopressin receptors. Vasopressin (and oxytocin) released after sex with the same individual time after time seems to essentially lead to addiction... in pretty much the same way that cocaine does.
The action of vasopressin was shown in field voles, which, despite the presence of vasopressin, were polygamous. Through altering the gene coding for vasopressin receptors in the NA, they were able to create pair bonding voles with intact families, loving relationships and mommies and daddies who adoree their little vole-lings.
This gene configuration and upstanding behavior are naturally expressed in the prairie vole.
Blah blahnonsense..
Bottom line is that, as Nathan said, humans tend to fall toward the middle ground on most issues. We’re not quite monogamous, nor polygamous… there’s a hell of a lot of flexibility to our behavior that isn’t quite there in other species. Most of our genes are not directly coding for proteins, but, rather, may regulate transcription factors..which operate to change whole slews of genes’ expression…
Our genetic inheritance has basically been toward flexibility, freedom from our genes. We have brains that… language, which.. social inheritance.. we can.. symbolism... contemplate existence.. we basically have no boundaries to what we’re capable of doing.
So yeah, I’d say that polygamy is as natural as anything else we do and if monogamy is what we want, we’re more than able to achieve it.
edit* bloody 'ell... someone seems to have already talked about my voles, beloved!