This isn't new (at all) and shouldn't be on Slashdot. This is email marketing 101. I do wonder if there's some deliberate astroturfing around this company.
Every marketing email you've ever received has a tracking pixel in it. This is why Gmail (and recently Y!) mail both added an anonymous proxy for loading images in email -- this means that not only does the sender not get your IP, but at most they'll only know the 1st time you loaded the email (subsequent requests are usually served from a cache). This is also why you should have images off by default in any email client (this is easy to configure in Gmail).
Before email clients added image proxy'ing, it was like the wild west.. any embedded images were served directly from the 3rd party host (including cookies, user agent, etc!)