I've never, ever hesitated in giving out my email address to anyone (that includes sites that I know are scammers and would sell my email address to anyone practically for the asking). In the past ??? years (since GMail was in beta), I've received less than 5 spams.

(I know it's a little irrelevant to your point though, but wanted to say at least with gmail you don't need to fear giving you email address out)