This is a great post about streams and emails.
From an organisational perspective, I like the idea that streams of information provide an opportunity for users to decide what information to tap into vs the top down communication that is email. This quote sums it up:
Looking at this as a 'wisdom of the crowds' sort of issue, it is more likely that information will be best distributed within any given group if each person can decide what information sources are likely to provide good information for themselves, rather than leaving it up to the sources of information to decide who should have access to it. This is the argument for openness in open societies, as well, and it has an immediate and obvious analog in the workplace.