Just found a really useful search engine for website owners:

www.copyscape.com

you can check that no one has purposely ripped your website and claimed it as their own (i.e. plagiarism).

I wonder if this uses similar technology to Google's "duplicate content" policy? It would be interesting to compare results.

http://www.bitscan.com also scans for copied web content and have a very easy to use interface.

copyscape: I tried a search for www.google.sk (cause .com , .co.uk and .nl were already over the 10 searches per month limit) and it returned a google sponsored search result for www.google.sk on a slovak portal site with only one of the search result being the same: http://www.copyscape.com/view.php?o=85720&u=http%3A%2F%2Fwww.zoznam.sk%2Fhladaj%3Fs%3Dwww.google.sk%26co%3Dzoznam&t=1204228439&s=http%3A%2F%2Fwww.google.sk&w=23&c=

And the same happens with bitscan.com for a google.com search. Guess they both forgot that search results always quote the original site.