The short: if I know you in person, and/or you'd like to hear things like "Hey Cat Stevens is really good" (more on that later) or "I like this particular blend of coffee at Victrola" or "I just saw a hat wearing a dog", follow @sedatesnail.
If I don't know you in person, and/or you'd like to hear things like "Huh, the ventromedial prefrontal cortex is involved in attention AND smell" or "git rebase --onto rocks the casbah" or "I wonder why nobody's studied the effects of lycopene on social networking", follow @dantasse.
The reasoning: AFAICT, there are two main uses of Twitter: to stay up to speed in your professional field, and to microblog about what you had for lunch. It's not that my "lunch" posts are super private, but it's just that nobody would want to read them. And given that we're all drowning in information these days, I want to try not to make people's lives worse.