Uh, I just realized this: if an on-line service requires more than an username and an email address to accept you as an user then you should not sign up.
An exception could be made for services that need to ship you stuff or seller you goods/service that you specifically signed up to buy... By otherwise, seriously, you should not sign up. And I'll try to live by these words.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko