When will desktop mashups be as viable as web ones?

This happens all the time, and another example came up this weekend when Ange was merging some photo collections:

“I love how Bridge lets me search for photos by so many great criteria, but iPhoto’s events are killer and the scrolling is so much faster.”

In the online world, the solution would be a mashup. (With the proliferation of APIs, do we even call them that anymore?)

Will there ever be a desktop equivalent? I can’t believe I’m pining for the promise of COM…