"If you log onto a site that has invested in software to track you, can they derive your email address from any of the info they gather?"

Jacob,

Yes and no. Via cookies, a site can track that it's you in perpetuity or until you delete the cookie... and some sites will leave several. Kill the cookie, and they don't know it's you unless you tell them again.

Generally, unless you specifically give a site your email address at some point (which they will record in your cookie), they can't just figure it out.

BUT: You probably have many cookies on your hard drive. If I wanted to write a particularly malicious web site, I could create a script that mined your hard drive for common cookies, hoping to snag an email address or other personal info. It wouldn't be that difficult and it would be highly effective since you pretty much have to have scripting enabled to surf anywhere on the web now-a-days.