This has been clear since I began reading blogs around 2000 and weblogs since around 1994. Via Dave3, comes Wired's tale of popular sites not being the source of the ideas found there:

The most-read webloggers aren't necessarily the ones with the most original ideas, say researchers at Hewlett-Packard Labs. Using newly developed techniques for graphing the flow of information between blogs, the researchers have discovered that authors of popular blog sites regularly borrow topics from lesser-known bloggers -- and they often do so without attribution.

On one hand this is obvious and on the other it is a bit shocking. But if you understand that the source and form of blogs as web logs, as opposed to personal diaries and the newer craptastic idea of "citizen journalists", was all about gathering what is interesting out there and repackaging it. As the reality of an aggregator is that it fixes what you read to your average list of 50 pre-set sites and deters surfing, the need for the original basis for logging the original material what you find see on the web becomes more important. Conversely, the aggregator and its sidekick syndication is the close friend of the "a-list" as it inhibits you from finding the sources for some of their best material.

Ditch the aggregator once in a while and surf.