Having finally gotten a nascent MySpace page to look like someone lived there, I started poking around. A rather handy browse facility allows you to perv the talent, filtering out those that don't meet your particular preferences. Which was when I remembered the survey results.
Intrigued, I set out to find what proportion of married people registered as UK resident were explicitly looking for dating and/or relationships (i.e. not just friends or networking - something potentially sexual) on MySpace.
Men declaring themselves married, stating that they were looking for dating and / or relationships clocked in at 35.5% - not far off the third of men reportedly "bored" in their marriages, or the 36% not getting enough marital sex. However - those were the men happy enough to have their photo (or at least a photo purporting to be them - some were avatars) online, generally those not concerned with being found out. Remove the requirement for a picture, and the proportion rose to 43.9%.
My curiosity got the better of me, and I refined the search to married men (with no requirement for photos) looking for dating / relationships who declared themselves straight (excluding gay, bi and "not sure") and the percentage dropped to 28.2%... a change of some 15.7% [of total].
Women declaring themselves married, while looking explicitly for dating and / or relationships were by contrast 26.4%. Again, these were those less concerned with discovery - with the requirement for a photograph removed, the percentage rose to 30.1%.
Declaredly straight married women (no requirement for photo) looking for dating / relationships dropped to 15.2% - a percentage drop of a similar order to the men, of 14.9% [of total].
I'm tempted to read into this that UK-based netizens of MySpace are more fluid about their sexual identity - particularly the women, of whom a greater proportion were uneasily labelling themselves "straight" - and not terribly concerned at the prospect of discovery. But of course such a reading filters out a myriad possible confounders, including laziness and ignorance in setting up one's profile, so interesting as such conclusions might be, they remain speculative.
Methodological note:
The age range allowed me a minimum of 18 and a maximum of 68 - presumably to prevent paedophilia and elder abuse - so anyone declaring an age either side of that was filtered out. Additionally, in trying to establish a total population, I drew the round number of 3000 each time. I'm assuming that to be the maximum hits the system can handle, but for the purposes of comparison and illustration, the number 3000 will be used as the "total population", despite its unlikeliness.
I also made no attempt to separate the sample into categories in line with Dave's original hypothesis, i.e. age deciles, particularly as data (am too lazy to look up references for this) suggest that younger people in the UK are less likely to be embracing marriage. This could reduce sample sizes, e.g. for the twentysomethings, to statistically insignificant numbers, rendering comparison meaningless. But if you're interested, go ahead and try! You'll need to sign up with MySpace first though...