Here's the phrase of the day: "continuous partial attention" Marc Eisenstadt has 12 years of email, and lots of detail on what it's composed of. Here's the interesting paragraph:
25 emails daily (and thereare many I know who have WAY more than this) is a lot to deal with, especially since the emails don't cluster evenly throughout the week. To get to a 25-per-day average, you're looking at more like 30-40 per working weekday, if you're the kind of person who switches off at the weekend (ha!). If each email requires 3 minutes of thinking/response time (you're lucky if you can average that), then you've got a guaranteed two hours straight down the tubes every day.

But wait a minute, "down the tubes" is incorrect: surely your emails involve key interactions, networking, brainstorming, appropriate drudgery and admin, in short what you get paid to do, right? Well, that's not clear... and requires drilling down a bit deeper into the data.

The analysis that follows, about midway down his post, highlights all the different facets of his email, which looks somewhat universal in the high-tech world.