StackOverflow is an extremely valuable resource for all programmers. I've not seen the option anywhere, but a yearly donation would definitely be something I'd do for a substantial amount (substantial to me as a student, so it's not the moon but not a beer either).
There's a word for this, it's called 'subscription' : )
They provide a service, you pay for it.
It's how most of the world works.
I think the underlying issue is price discrimination: how to get the large numbers of those unwilling/unable to pay some value, while providing value to the higher order users as well.
It's a paradox that people will pay more for a coffee than they will something that can help them substantially :)