Facebook has addressed a big chunk of these very important issues w/ friend lists. I have about 400 FB friends and ~40 of them in a list of "Real Friends" - i make that my main feed and i only see status updates from them on my homepage. hopefully soon that filter can be applied to the highlights section too. when a new request comes in, FB asks if i want to add it to a list as part of the accept process. i suspect we'll see more granularity in terms of applying permissions to groups to address some of your other very valid concerns. I'm about to make another group called "business only" for people who i don't want to reject their request and alienate, but also don't really want them seeing any of my personal updates - the situation you describe with the persistent contact of yours.
Not exactly the same type, but have you read The Pillars of the Earth?
wrt to Twitter specifically, I've been thinking for a while that there are two different businesses here w/ very different use cases and requirements. One conversational in nature, one broadcast. I don't think there's anything inherently negative about that, it just makes social dynamics a little muddled when they are both combined in one unified platform.
looking forward to seeing what you're up to, Pete! Another one worth taking a look at is Gist - they are doing some interesting stuff. In webmail, Zenbe is innovative. And Xoopit is doing a lot around images/files in email.
i somehow completely missed the first line of your post.
Also, I'm guessing you watch Californication?
BTW, all the little things really add up. Changing a double latte every day into a regular coffee or Americano is a delta of almost 2 pounds worth of calories in a month.
Brad, I second Dov's comments about SparkPeople being a great site. It is especially useful and addictive if you're a stats/information junkie.