I've noticed a few sites out there now that allow you to search the Google Analytics and/or Ad Pub ID and discover what sites use the same code.
For example, if I'm running adsense, I can search on the adsense pub id and find all websites using the same id. From this information, I could tell what sites an individual/company owns.
Is there any way to block this? Perhaps they are getting their information from some search engine out there and if you blocked that search engine, you would effectively block the tool? (as long as it's not a big SE)
You can have a dedicated IP, whois block, dedicated IP, but with such services, you would also have to have unique accounts (like analytics, adsense, etc.) for each domain...