I typically enter my email address in a form that cannot be harvested by a computer, but can be read by a human, e.g.

"johnsmith at earthlink dot net"
"foobar at hotmail dot com"

However, this is not possible on FlyerTalk, since changing your email address causes a new password to be sent to the new address, and I guess you'd get locked out of your account since you wouldn't be able to find out your new password.

As an alternative, you could put your email address in another field, such as "Interests".