Search warrants have to be very specific regarding what they target. "Give us all the records for those who searched for 'murder' related queries" isn't specific enough for a warrant. "Give us the records of [some user] searching for [terms related to some specific technique of disposing of bodies] during March 2009" might be valid, but IANAL.

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.

It would usually have to be even more specific than that.

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 :)

And why don't they do the same with DNS queries?

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?

They delete them, but not before the government makes a copy.

Are you serious? If so, any further info?

No, I was just joking. I planned on indicating that, but I forgot to when I left the browser tab for a bit and returned.