Not sure what happens that makes Google decide to remind people of their own website when people search for other brands, but when I search for Istockphoto the top of Google's SERPs say "Tip: Looking for pictures? Try Google Images".
What next? Search for eBay and get "Looking for auctions? Try Google Base."
Search for Amazon and get "Looking for online shopping? Try Froogle."
Pretty sleezy tips Google, IMHO.