Bazaarvoice uses Rackspace's Dallas data center, with Internet content provider Akamai as its back-up provider.

"The advantage of using someone like Rackspace is that they are experts in physical hardware and network management. We would have to invest a significant portion of our engineering time toward that, and we didn't want to have to do that,'' Maag says. "If we ran our data center, physical space would become a concern when we're trying to scale like that.''

Maag says the fact that Bazaarvoice uses Rackspace's data center rather than running its own appeals to its largest corporate customers.

"Rackspace lends us a lot of credibility,'' Maag says. "Every client is concerned about where our data resides. It's a lot nicer to say that we host our machines at Rackspace,'' which runs data centers that are certified to meet SAS 70 security requirements.

The arrangement helps Bazzarvoice keep its internal IT staff down to only two of its 200 employees.

Our internal IT is working on only a handful of things, such as keeping people's personal machines up and running,'' Maag says.

In April, Bazaarvoice announced that it has served more than 10 billion user-generated reviews. The company launched its service in January 2006.

"We'll probably be at least doubling again in the next year'' in terms of the number of servers it rents from Rackspace, Maag adds. He says he is considering migrating Bazaarvoice's Exchange e-mail service to Rackspace, too.

Another company that plans to increase its use of outsourced data centers is Wall Street Systems, which uses Savvis for its corporate network infrastructure and to support its software-as-a-service offering. Wall Street Systems provides treasury and high-performance transaction-processing software to financial institutions.

"We're using Savvis' utility computing framework to deliver our solutions to our clients,'' says Mark Tirschwell, chief technology officer of Wall Street Systems. "We've probably tripled the amount of infrastructure that we had a year ago from Savvis. . . . We were originally using some shared Savvis components, firewalls and things like that, but now we have our own dedicated firewalls and our own dedicated Active Directory infrastructure all managed by Savvis.''

Wall Street Systems uses Savvis as its corporate network and to provide e-mail, videoconferencing, voice over IP and standard data communications to its 500 employees in 12 countries.

But it is seeing more significant growth in its use of Savvis' data centers to support its software-as-a-service offering. Wall Street Systems uses two Savvis data centers now, but it expects to add two data centers in Europe during the next year.