There's trouble brewing in Kentucky, as two lawyers (who ironically specialize in ethical issues) square off over sponsored links on Google purchased by one lawyer. It seems the lawyer purchased ads so that whenever someone searched for his competitor by name, his own name would appear in the search results.
This reminds me of the days when lawyers had to worry about competitors inserting the other's names into the metatags of the competition's website. As I recall, there were a few lawsuits finding the practice to be a violation of copyright -- but I don't think the issue was ever considered on ethical grounds.