Vendors hawking them include the likes of Hewlett-Packard Co. and IBM, Linux purveyors Red Hat Inc. and Novell Inc., and independent support providers such as SpikeSource Inc., OpenLogic Inc., SourceLabs Inc. and many others.

Yet a growing number of critics say that stacks has already become a hyped-up buzzword that fails to serve many users.

"Stacks are rigid and deterministic," said Winston Damarillo, CEO of Simula Labs Inc., a Marina Del Rey, Calif., open-source software provider. They are "prefab solutions, which most customers don't really want in the first place."

Take Davis Tharayil, CIO at Home Insurance Co., for example. Tharayil is looking for a cheaper alternative to the Oracle databases on Solaris servers the in-liquidation insurer runs now. Tharayil is testing a custom server appliance built by rPath Inc. with the open-source Ingres database running on a stripped-down version of Linux. Even though Tharayil was looking for a plug-and-play product, at no point did he consider a precertified open-source application stack.

"A full stack just wasn't necessary," Tharayil said. Besides, he added, "I've been in the business for 35 years. Every time something new comes along, they say it's a silver bullet. And I still haven't found one."