There is a Slashdot article on Grokster.com changing their front page to one which displays your IP address and notes that it has been logged. As noted in many comments on Slashdot, I’d just like to say that this is no different to ordinary browsing: the web server always gets your IP address, otherwise it wouldn’t be able to send data back to you.
And usually, this address is logged with each request. There is nothing new here, and this site is just a scare tactic to put off people who don’t already know this.
It is important to draw people’s attention to this as some may believe that the site is doing something untoward, in order to obtain an IP address. In fact, any TCP connection (except spoofed packets) results in the server-side application being able to determine your IP address.