Twitter also has this element of being like a river you can dip into whenever you're inclined and ignore the rest of the time. As you say, I do subscribe to some newsletters and mailing lists but it's very easy to get overloaded and/or end up filtering things to a folder that you never look at. Twitter seems to strike a reasonable balance of utility/effort/distraction/etc. for a lot of things that email-oriented methods really don't.

Ah right.. Like that story last week about the writer that got so addicted to twitter that she had to close her account? From my point of view it doesn't seem so easy and balanced.

I'm missing something.. You just said that you won't click a button to signup a newsletter that delivers you funny jokes and the tour dates of a random comedian, but you are more than happy to press a button to get exactly the same things but with the limitations that the funny jokes must be less than 140 chars. There must be a reason if I never used and understood twitter at all..

Emails require more of my attention and they arrive whenever they are sent. Tweets require zero attention, they are easy to ignore, and I never see them unless I specifically seek them out by opening Twitter. Basically Twitter is much more voluntary than email.

I get this, but it's kind of funny to hear someone say Twitter's unique value proposition is that you can ignore it. As a non-user I must be extracting tons of value from it then! It's the poor users I feel sorry for!

Just joking around. But, not completely. The value you speak of is really the ability to spend your time on something potentially more worthwhile. People forget social media has an opportunity cost.