This subject has been raised before but I feel it is a topic which should be revisited periodically if only for the sake of new members. (One member just contacted me privately about his GF checking up on him.)
Anyone who has acquired your e-mail address can apply for and get a complete profile of the surfing history associated with the IP for that address. There are multiple sites which offer this service usually for a fee. Everything you do over the internet can be traced in this manner and used for any purpose. To provide anonymity it is essential to acquire protection. A good site to visit: http://www.thefreecountry.com/security/anonymous.shtml
Some of the members who are more versed in this area, e.g. techman, I am sure, can provide greater detail. This can be pretty serious stuff for anyone who might be vulnerable in this area.