In social games I always did. Early on in school cricket, I never walked - there's too much pressure on you and you don't really understand the value of it when it might mean losing a game (or your place in the team). Later on I did, and as an international player I would like to think I'd walk. Bad decisions annoy me, and they affect games - sometimes very severely, and contrary to some opinions, they don't even themselves out. If I don't walk when I know I'm out, I'd be a willing accomplice to that process. I realise that I can also receive bad calls where I'm incorrectly given out, but I'm a victim of that situation, rather than a willing participant. In the long run, I just believe it's better for the game. I'd make an exception for LBW calls, even if I knew it was really close. If I can't know for absolute certain myself, it's in the umpire's hands.
The fact is though, that it's not really so simple at professional level. Consistency, and whether or not I receive bad calls against me isn't really that important an issue for me, but money might be. An interesting secondary poll to this might be to ask people if they'd walk when they had a family and children, dependent on their income from cricket.
Let's say this is the case and you've had a bad trot and you're in danger of losing your place in the international team. You nick one through to the keeper, but the umpire hasn't heard it. Do you walk, for the good of the game, or do you remain at the crease, and put your family's welfare above what is ultimately, just a sport?
Surely it can't be that easy to instantly say "yep, I'd walk" like some of us have.