Human multitasking and computers

Humans start multi-tasking (to their detriment) when sitting in front of a computer, because computers are too slow - more precisely, are not responsive enough. Of course, I have only anecdotal evidence for this.

E.g., when I'm reading a book, flipping the page is subjectively immediate. Not so when browsing the web. There is a perceptible lag between pages and that gives time for the attention to stray. (I'm talking about subjective time here, this may not be borne out in real time.)