I started doing some of them more as an amusement than for the $$ when I was down to some medical issues.
First rule, if they want $$$ just run right there.
That being said, even though I am back to work and making pretty good money I still do them, and the 'paid email' as well. Not really sure why, other than I figure if I am going to get spammed to death, I might as well get paid for it. When it gets right down to it, I would be surprised if I am actually getting $3 (US) an hour... but on the grounds all Im doing is having a beer and winding down from work.. why not.
Do set up a seperate email for these things... I think my yahoo account has over 16000 spams in the junk box (their filter seems to work best) for just this week.