Google is a registered trademark, Googlebot may not be registered. However as it clearly is affiliated with Google, even if Google had not registered it they might pursue claims.
I am not familiar with U.S. law. If the courts in U.S. adopt a strictly formalistic approach on using names in a business context, then the results may be different.
However IMHO, Googlebot is clearly associated with Google and anyone who uses Googlebot as their User Agent is tricking the sites owner's into believing that the request was made from Google.
As for legal grounds, Google could sue on unfair competition.
I am not familiar with U.S. law. If the courts in U.S. adopt a strictly formalistic approach on using names in a business context, then the results may be different.
However IMHO, Googlebot is clearly associated with Google and anyone who uses Googlebot as their User Agent is tricking the sites owner's into believing that the request was made from Google.
As for legal grounds, Google could sue on unfair competition.