A few days stale, but worth reading is Greg Linden's summary of why apps shouldn't ask people about preferences. A modern app should watch what they do and then divine the rest. I take it that doesn't mean "don't help people get things done", but don't ask them to explicitly rate stuff, or maintain preference data, or respond to repeated off task queries.
I think this is the direction Aggregator 2.0 will eventually have to head. For a number of folks, maintaining blogrolls and the generated flow just won't work. People who need to read tea leaves like business intelligence analysts, political operatives, public relations, cool hunters, etc. etc. I'm still working out the profile, but people who have to observe communications in fast changing environments where trusted sources may not even exist.
The trickiness is that some of what will be needed is social information. This leads to needing critical masses of people buying into new infrastructures. The only obvious way to do that is through Web interfaces and plumbing, which unfortunately makes it somewhat more difficult to watch what people are doing.