According to the just released Gartner's 2006 Emerging Technologies Hype Cycle, mashups are nearing the hype cycle peak. They get a rating of "moderate" and Gartner's analysis is that:
Mashup is rated as moderate on the Hype Cycle (definition: provides incremental improvements to established processes that will result in increased revenue or cost savings for an enterprise), but is expected to hit mainstream adoption in less than two years. A "mashup" is a lightweight tactical integration of multi-sourced applications or content into a single offering. Because mashups leverage data and services from public Web sites and Web applications, they’re lightweight in implementation and built with a minimal amount of code. Their primary business benefit is that they can quickly meet tactical needs with reduced development costs and improved user satisfaction. Gartner warns that because they combine data and logic from multiple sources, they’re vulnerable to failures in any one of those sources.