Here's an excellent video that's must-viewing for anyone who uses tools like, say, Google, in research or teaching. The phenomenon described is also something to be aware of as our students use these tools for class research. The overall consequences for civil society seem potentially significant as well.
The speaker, Eli Pariser, is one of the brains behind MoveOn.org, and he's got a new book out called, appropriately enough, The Filter Bubble.