The first is Amazon's use. Here is Jeff Bezos' wishlist as an RSS feed with SLE.
Then there's eBay - this RSS+SLE feed provides filtering and sorting on a number of different categories:
Yahoo! Music has been experimenting too. Here is the Yahoo! Music Top 10 Songs list in RSS+SLE
More links including videos over at the IE7 team blog.
-Tags: RSS SLE Microsoft Mix06 IE7