It's pretty clear that if you're targetting non-US countries then hosting in the non-US country improves your rankings for that country.
What about the other way? Say there's a US targetted website that already ranks well for US searches - but the site's not hosted in the US.
What sort of returns would one expect from simply moving hosting to a US location? Would rankings improve noticeably?
I have a friend with this situation, I'm considering calling him and recommending he move his hosting to a US account somewhere.