I am fascinated by the data websites collect when you simply visit once, for however short a time period. One little click and they build your profile. And, when you use sites regularly they gather an all-out tome of information on you.
Facebook makes suggestions for friends you may know via your other friends (the VAST majority of which I do not) or groups you may be interested in following.
Amazon suggests products you may be interested in, not just from what you’ve purchased in the past but also from any number of products you’ve simply browsed.
Yahoo sends out E-mail alerts on any number of topics based on your searches. This one really had me tripping the other day. Sure, seeing a message from Yahoo! Sports or Yahoo! Finance or other topics is normal for me. But the other day Yahoo! Fashion popped up in my inbox. What? Clearly it’s time for me to update my profile with a picture of myself instead of the generic one – then I’m sure they’ll learn that fashion is the furthest thing from my mind.