I have been worried about this for a while (see this post from Dec 2006 and way back when in August 2005 when I first was alerted to this issue) Just when things were looking really grim on the online privacy front this ruling came in…..from Wired Blogs:

The ruling by the Sixth U.S. Circuit Court of Appeals in Ohio upheld a lower court ruling that placed a temporary injunction on e-mail searches in a fraud investigation against Steven Warshak, who runs a supplements company best known for a male enhancement product called Enzyte. Warshak hawks Enzyte using “Smiling Bob” ads that have gained some notoriety.

The case boiled down to a Fourth Amendment argument, in which Warshak contended that the government overstepped its constitutional reach when it demanded e-mail records from his internet service providers. Under the 1986 federal Stored Communications Act (SCA), the government has regularly obtained e-mail from third parties without getting warrants and without letting targets of an investigation know (ergo, no opportunity to contest).

It is sort of odd that it is about penis spam but hey – freedom is freedom is freedom.
To reach its decision, the court relied on two amici curiae that presented compelling arguments for shoring up current privacy law with respect to e-mail. The article is worth reading in full.