"Good fences make for good neighbors," he said. "This is not a religious issue, but a very practical one."

But critics claim cross-licensing is a sneaky attempt to get open source vendors to de facto admit that their software does violate Microsoft patents. Not that they think it actually bolsters Microsoft's case.

"The signing of cross licenses does not mean that the patents are valid," Radcliffe wrote. For instance, licenses can be signed "for a variety of commercial reasons to reduce risk" or to give one Linux vendor a perceived edge in the market.

Jones is more blunt. "I am not aware of any relevant Microsoft patents that have been court-tested. That would be the only way to strengthen Microsoft's claim that there is anything actually infringing," she wrote. "All they have proved is that some will cave rather than find out in court."

The last Linux patent protection deal Microsoft inked was more than half a year ago, October's deal with TurboLinux.

But Gutierrez promised more cross-licensing/patent protection deals soon. There are "ongoing discussions with U.S. software makers," he said. "They just can't be timed from a PR perspective."

Gutierrez thinks even a vocal holdout like Red Hat will eventually come around, once they "recognize that there are opportunities that they are missing out, as customers are increasingly demanding vendors come together and tackle interoperability challenges together," he said.

Red Hat did not reply to a request for comment. But Groklaw's Jones is skeptical.

"The world wants openness and interoperability, up to a point," she wrote. "I don't know anybody who wants to interoperate with Vista."

Moreover, "Red Hat is making money at least in part because it *didn't* sell out to Microsoft, in my opinion," she continued "Even if they [Microsoft] had a valid patent, going after Red Hat is like threatening to kill Dorothy's little dog Toto. You can't do it and have people like you."

Radcliffe argues that the heterogeneity of products -- that is, Microsoft and open source software -- in most corporate networks, which Redmond asserts leads to increased demand for interoperability, also immunizes open source vendors from Microsoft's legal threat.

"Most Linux users are not concerned about this threat," wrote Radcliffe. "Since they are also Microsoft clients, they believe it is unlikely that Microsoft will sue their own customers. We have not seen a significant shift from the 'licensed' Linux vendors to the 'unlicensed' ones."

Todd Weiss contributed to this story.  Computerworld is an InfoWorld affiliate.