CAMBRIDGE, Mass. -- Software as a service continues to be rapidly adopted by American enterprises, according to Forrester Research. The technology formerly known as application service provider is now in place at 16% of North America's largest enterprises, up a third from the previous year, the think firm found in a recent survey of 1,017 technology decision makers. Forrester found that the rate of SaaS uptake on this side of the pond is twice that of Europe and that human resources, collaboration and customer service relationship software are the hottest areas. Drags on adoption, Forrester said, are integration, customization, security and cost concerns.