Here are some more bulls from that page, which pretty well speak for themselves. Has anyone ever heard of "web beacons" before this? I hadn't -

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Yahoo!'s practice is to include web beacons in HTML-formatted email messages (messages that include graphics) that Yahoo! itself sends in order to determine which email messages were opened and to note whether a message was acted upon.

Occasionally, "Yahoo!-Delivers" messages may award you Yahoo! Points upon opening the message. Yahoo! Delivers messages include a web beacon that displays a message informing you of this award or inviting you to join Yahoo! Points if you are not a member.

Yahoo! Points may be awarded when you act on a banner or message offering points for visiting an advertiser's web site. The advertiser places web beacons on their page to allow Yahoo! to award you points for your visit if you are a Yahoo! Points member.

In general, any electronic image viewed as part of a web page, including an ad banner, can act as a web beacon. Advertising networks that serve ads onto Yahoo! may use web beacons in their advertisements.