who'd have thought I would write this blog post

Detailing the vocabulary and usage differences between American English and UK English would take a blog entry far larger than I would ever aspire to write, but here's one that struck me the other day: the Americans use the phrase "who knew?" pretty much exactly where we in the UK would use the phrase "who'd have thought it?", most often as a little spicing-up interjection tacked onto the end of another sentence. Until you've worked out that that's what it means, certain news headlines and blog entry titles can look oddly alien, such as these two sporting ones (both about ice hockey as it happens), or these two telling you to, respectively, visit Toronto and steer clear of Eritrea. Many more random examples are available in the blogosphere, for instance here, here and here.

In both UK and US versions the idiom can mean either "I was somewhat surprised to learn this" or "I was not at all surprised to learn this", depending on whether it's being used ironically or not. I suspect there are examples of both in the links I've given you, in fact I would guess the ironic usages outweigh the non-ironic ones. No clues though!

Counterexamples of the UK usage can be found here and here, in fact the phrase is so ingrained in UK culture that we even have pubs named after it.

I'm not saying there's an absolute divide, and that you can pin-point someone's nationality from which idiom they use, but I suspect you wouldn't be wrong often if you tried. I would guess that while there may be some Americans who use what I'm calling the UK usage, there are very very few people from the UK who use the American usage, unless they watch an enormous amount of US TV or spent an inordinate amount of time on the internet. This sort of asymmetrical intersection between two sets precludes me drawing you a Venn diagram, unfortunately, otherwise I would.