5 activations on different hardware for 6 months (then you get new 5 activations)
And of course you can always email support if you have any problems, but I think with 5 for varying hardware over 6 months you'd have to be extremely rich to keep upgrading your PC that much
Regarding paying VAT, I believe it's only if you live in the EU that you pay VAT, but you could be in the US and pay with an EU credit card and that would mean you don't need to pay VAT.
Of course the postcards/map would be sent to the non-EU address you register with, so if for example you're a European, visiting a non-EU friend, and you order ArmA2 from Sprocket with your EU credit card, but then suddenly have to return to Europe before your postcards/map arrives, as long as you correctly entered the friend's address he will still receive the postcards/map and can forward them on to you.
---------- Post added at 21:41 ---------- Previous post was at 20:46 ----------
And for those worries about download speed: