I think some of you already know http://spyonweb.com which is a tool to explore, investigate, ok let's say it SPY on your competitors.. It has a database of domain name and for each it tracks the public identifiers such as AdSense ID, Analytics ID, server IP address, etc..
Well it's not a perfect tool, but with the help of similar sites you can get an idea of what your direct competitors are up to..
Personally I think it is fair to use it and see what others are doing, we're not alone, but important information is not shared easily, so we have to study on our own and that's what those tools are for..
Here are a couple more tools like SpyOnWeb you might like: http://www.best-reviewer.com/best-review-top-3-sites-similar-spyonweb-re...
What tools have you successfully used in the past? Care to report on useful tools related to our AdSense business?