I make a point of providing what could be considered pointed feedback on their spam-feeding mechanisms formatted as obviously fake-but-valid-looking email addresses. If shortsighted jerks want email addresses, I'll give them some.

What I actually want for this sort of problem is a browser extension that allows me to annotate domains in some way, and then treats links differently based on that. This is a half-baked idea; I have no time to make this, so I haven't been thinking about it much. (Please steal the idea!) But perhaps a way to quickly tag domain names - 'annoying popup', 'spammer', 'dead to me', etc., and then indicate the tags visually next to links/change the colors/something like that, so I can more easily avoid sites that annoy me.