Found a web service that allows to search all web sites by same owner, or by google analytics ID. It links sites by Google Analytics ID, Google AdSense ID and other IDs like Kontera and YPN - showing all sites containing the ID of the site in question.
They claim it's possible to find blogs of your competitors.. That's quite possible, I tried several sites run by people I know, and it really listed all their sites, even they've never told me about. It turns out one of my competitors bought 3 additional domain names for their site (but since they were absent in google search results on keywords I considered important, I didn't know about those sites).
That's nice, before this service, it was possible to search for sites only by domain name owner data (but due to popularity of private domain registration, it was becoming obsolete).