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webjourneyman - 2:02 pm on Jul 30, 2006 (gmt 0)
Google registered the trademark Adsense in 2003 according to the Patents and Trademark office www.uspto.gov. It seems to answer my own question. A corporation (even one as large as Google) can not demand a domain name that has been registerd before they register it as trademark.
In light of this discussion it is interesting to check out the website www.adsense.com, registered as url in 1997 according to whois.ws.