And annoying other players can be very useful! I personally struggle internally with the ethics of intentionally winding up the oppo (like I should worry about ethics when there's $$$ involved ), but there's no doubt that anything that blinkers your opponent one way or another can act in your favour.

Of course, it can backfire - making a pssive player more aggressive can caus no end of trouble - not only do the start attacking the bluffs you've been getting away with all game, but he suddenly finds that aggressive play is winning him pots!

Having said all that, I hate really slow players, people who don't auto-post blinds and take the full countdown to bet post-flop. Maybe some of them do it on purpose, I don't know. But I tend to mark them down as unprofessional, and am more likely to treat them with disdain - until, of course, I get my fingers burned (and there have been 2 or 3 of them for sure).