I suppose I'm one of the Monday types. I think it does have to do with how you visualize time. But it is worth noting that a fair amount of the language we use to indicate time is ambiguous at best. For example, today is Thursday. If I tell you that I'm going to get you the report next Friday, that is generally taken to mean a week from tomorrow, even though tomorrow is the next Friday. This has always been a pet peeve of mine, considering that saying that a week from tomorrow is the "next" Friday implies that tomorrow is the "current" Friday, which makes no sense as it's not Friday! It would almost be like if I said I'd deliver the report on the next 14th of the month, and then delivered it in mid-September. I'd get my ass fired for that one, and rightly so. But it seems like the "next Friday" construction isn't going anywhere in American language, and this country's Orwellian neglect of language will continue.
Mark Fraunfelder of Boing Boing asks: Let's say a meeting, originally scheduled for Wednesday, has been moved forward two days. What is the new day of the meeting?
Friday, of course. It took me a few minutes to even understand that another answer was possible. Alex Tabarrok was also confused by the idea that there was more than one possible reply. But he thought the answer was Monday.
Interestingly, the Spanish language doesn't have this particular problem. In Spanish, you basically say "this coming Friday," which eliminates the ambiguity nicely. Just another example of why English basically sucks.