The Economist, April 12, 2008, at 8, sketches three addictive features of Blackberry use (or any PD). Since I have turned to the theme of destructive PDA-fixation before (See my post posts of April 3, 2005: productivity increases from PDAs, July 14, 2005: diminished productivity; June 5, 2006: workplace stress caused by them; Oct. 19, 2005 on telecommuters and PDAs; and Dec. 16, 2007: competing for attention against a Blackberry.) I mention each of them below.
Random reinforcement lures us on because every now and then among the dross there is gold. Second, the illusion that more information always leads us to better decisions means that we keep reading for that extra fillip of insight. The third reason is impression management, because we want our superiors to know that we are ever vigilant, never sleeping or on holiday. The hook slips further into the throat.
Obsessive use also engenders multi-tasking, or at least multi-something, which diminishes productivity (See my post of Feb. 8, 2008: five references to multi-tasking.).