Re: I guess ... not many, but waaay more than "none"
"and lost customers from those who can't be bothered to complain and just take their money elsewhere"
Oh hell yes.
There's a dash, it's invalid. Really? There's an unrecognised domain (.eu), it's invalid. Really? The name part is too long (no, it's a spam trap address with their name in it), it's invalid. Really?
The good sites actually send an email to the given address once to "verify my account", the bad sites choke. And, of course, if they aren't willing to accept my email address for notifying me of the status of my order, well I guess I'll just have to take my order elsewhere.
For what it is worth, it is usually American sites that display this incompetence. The same sort that let me pick a country from a drop-down list but then choke because the zip code is invalid/missing, and after wading through loads of pseudo-legalese it says in small letters that they don't ship overseas. Well, why didn't you say that when offering a country instead of wasting my time you retarded assholes...
Still, between that and the price USPS wants for sending anything, it is getting to be cheaper to order from anywhere else on the planet.
tl;dr version: random rant about incompetent online ordering