I get hundreds of visitors each day with Google in the referrer, but no keywords. Most of them are from foreign locations and/or foreign Google domains (example: google.be).
An example referrer:
[
google.be...]
num&source=web&cd=6&sqi=2&ved=0CE8QFjAF&url=http%3A%2F%2Fwww.#*$!#*$!#*$!.com%2Ff79%2Fpagename.html%2F&ei=mRqRT9b-FYfD0QWS8ezXAQ&usg=AFQjCNFM0yFkWTCnYFto_
5BYv7GpzeQQlw&cad=rja
Are these valid referrer strings?