Gmail's Terms of Use do state in Section 3 that:
First, if you feel that you are in danger, we suggest contacting your local authorities. For nuisance emails, we suggest setting up a filter in Gmail to send mail from the sender directly to your trash. If you have a Gmail address, please read How do I set up filters? for instructions.
Because message headers and senders can be spoofed using a variety of means, we're unable to take action on any user without further verification. In accordance with state and federal law, it is Google's policy only to provide information about a specific Gmail user pursuant to a valid third party subpoena or other appropriate legal process.
We apologize for any inconvenience, and we're sorry that you're receiving such messages."