Also this applies to bounties who asks for registration to their websites, this could be attempt of stealing your details.
Honestly, I wouldn't trust half of them, and would be using a disposable email. But, that's just me.
I wouldn't also , if i have to I make new email to register with them.
I think that warning about this should be included in original post, since a lot of users do not know this or just haven't thought about this problem.