If you are stupid enough to use your real identity and location on Facebook and further communicate any incriminating information on Facebook — you are guilty of being a total asswipe ... Any public posting is "plain sight" evidence — no warrant is needed for that.

However, without a warrant, none of the information obtained in a search of your Facebook account is admissible in any US Court. Maybe, there are ways to do so under the US PATRIOT Act.

Information gathered this way may not be used in a court proceeding but if not brought to light could be used "unlawfully" in any police or government investigation. This is done all the time if you are not aware of it ...