lifegoes Congratulations, what's he like?
RegisDead You don't have anything to lose by asking him out, do you? although if he turns you down you WILL end up bumping into him in ASDA every time you go for months
I have sent Mr Urbanite a message saying I'm perplexed by his long silence, but I suppose I could see if there are any tickets for the gig left...
just throwing this out there but when you say he went quiet on you for 12 days, I'm assuming you went quiet on him too? Or were you messaging him and he was ignoring you?
As much as it's a bit odd that his messaging pattern changed so suddenly and you'd be wise to be slightly cautious I also think that while you're only in the chatting phase there should be no expectations. The people at the other side of the screen have their own lives and stories going on. Without wanting to sound harsh, they owe you nothing and can't be expected to make you a priority before you've even met.
Hmmm....I agree up to a point, wishywashy. He has had gaps in communications before. And that's happened with other irons I've been chatting with, and been fine. However, when you've been talking for a while, and you've made plans to meet up, and then they go quiet...it strikes me as odd that you wouldn't think "Wow, totally overwhelmed at the moment, but I should just drop crack a quick message or she'll think I've ghosted her".
On the totally other hand, the massively overinvested- seeming bloke I've been chatting to for a couple of days has done a massive flounce because I didn't text him for a whole FIVE HOURS between 11.00 am and 4.00 pm today. He "needs someone to seem interested", apparently. 
(bangs head on table)