I'm late on this, but BIG kudos to the Popfly team for having the sole Microsoft entry in PC World's Top 25 Most Innovative products!
Here's a snippet from the article:
Innovation: Lets you use Microsoft's Silverlight platform to create Web mashups.
Benefit: Though Popfly is still in early beta, its operation is clearer and its display is more attractive than that of the similar Yahoo Pipes tool.
If you ever played with Legos as a kid, then you should be able to assemble a Web mashup in Microsoft's Popfly. No coding know-how needed--using Popfly is as simple as choosing content sources (such as pictures, video, or news feeds from various online sources) and connecting them to a display model (such as a video player, a dynamic box for text, or a game of whack-a-mole that pops up pictures, for instance). Voilà, you have your mashup. You can embed the resulting creation in a blog entry or Web page, or just share its URL so others can admire your work.