Philadelphia- Heard the one about the folks from Philadelphia who say they lost $500,000 on an Internet porn site?

It’s no joke. Their company filed suit over the matter in U.S. District Court in Philadelphia – in a document that also reveals the purported market value of a Web site with the domain address www.sex.com.

It’s worth $11 million.

“A domain name can make or break a company,” said Robert M. Silverman of Ambler, a lawyer for Philadelphia-based Sex.com Inc., which filed the lawsuit. Silverman declined to identify the local owners.

“These intangible assets have so much good will attached to them and are so recognizable,” Silverman said. “It’s no different than back in the 20th century, when a jingle was everything for a product.”

According to the lawsuit, filed yesterday, Sex.com signed an $11.4 million deal last month with a Boston domain company to acquire the Internet address www.sex.com.

As part of the deal, Sex.com alleged that it made a $500,000 deposit to Web site broker Domain Name Acquisition Group L.L.C., the defendant in the case.

The civil complaint did not say why the deal fell apart but alleged that Domain Name engaged in “repeated untruths regarding the domain name Sex.Com, about other competing offers for the domain name Sex.Com, and various other material and relevant exaggerations and untruths.”

Domain Name president Andrew Miller said he had not yet seen the lawsuit and therefore could not comment. The case has been assigned to U.S. District Judge Bruce Kauffman.