My search history probably makes me out to be a psychopath, when in fact I just have a wide array of strange interests.
If you're ever brought to trial using evidence gained by a warrant which didn't list that evidence to some reasonable specificity, any decent lawyer will have that evidence removed from consideration.
i.e. they would probably have to specify what they were looking for as well as some specifics of why they think X user (IP or google username) relates to Y person in their investigation.
Were forgetting, I think, there is already wide provisions for law enforcement to get your email password.. no one ever gets het up about that in the same way but most of the big ISP's can be forced, with warrants, to hand over access to accounts :)
Quoting from the recently released public DNS service:
"The temporary logs store the full IP address of the machine you're using... We _delete_ these temporary logs within 24 to 48 hours."
http://code.google.com/speed/public-dns/privacy.html
Is there anything in the Patriot Act that says explicitly that search engines should keep search logs but not DNS queries?