I recently got involved in a Twitter discussion over the merits of Twitter hashtags vs. Google+ Circles; at some point I said that I liked better the former especially when coupled with an efficient single stream reader like Hootsuite, but both were missing a crucial NOT operator and this remark was not clear to most discussion participants.
Since I found hard to explain it in 140-char morsels, here is my reasoning.
Lists and Circles are essentially boolean OR operators: they create streams that are the sum of all individual contributions by List or Circle members. Now imagine I have a “Bloggers” Circle or List and Robert Scoble or Joichi Ito are part of it. Their volume is probably 10x any other blogger and therefore “drowns” other contributions; if I had a NOT operator I could create another stream that is made of the Bloggers list/circle minus Scoble or Ito and therefore focus on contributions by others.
Moreover, imagine this morning I didn’t want to read stuff related to the Academy Awards: had I a NOT function I could form a stream with -#oscars to achieve my desired outcome.
Hashtags are a dynamic OR that is less permanent than a list and does not require I know the handles of people, and as such is extremely useful, but only if I have a multiple column client like Hootsuite or Tweetdeck where I can separate e.g. all the stuff that’s going on e.g. at a specific event. Here, too, a NOT function would allow me to further refine a high-volume stream to identify trends and follow conversations.
Probably a similar case can be made for the AND operator, and in general the need for differentiating permanent (on the person) operators from dynamic ones (on the stream).