Yahoo! just launched a new mashup tool called Yahoo! Pipes. The tool allows geek-savvy web users to wire together content filters without writing code. On quick glance, the system reminds me of the way that Apple's Automator empowers users to create scripts without writing any AppleScript--only this tool is for wiring together web content. It's certainly an idea who's time has come. Even if it doesn't attract mass usage, it will be successful if it inspires a new level of user control over content, or perhaps a new generation of web tools.
There's enough detail on the Pipes' site to get a feel for it, but you might also check out the O'Reilly Radar post, "Pipes and Filters for the Internet" for more.