You should obviously be taking a little bit of time to consider your hand, to try to put your opponent on a hand, as well as the board and the action in front of you before determining how you proceed. As my hand improves, I think it is important to still take a little time before acting. We still need to consider what how we want our opponents to react to our action, whether we want them to call or fold, or how strong we want to appear.
Of course the speed at which we act gives a lot a way about our confidence in our hand. We know that acting fast can be an indication of strength. Whereas, taking a long time to act could indicate a lack of confidence in our holding. Sometimes I want to make an obvious snap call like Rob Salaburu, where my calling chips beat your betting chips into the pot, as a show of strength. More often than not, I want to play at an even tempo that gives nothing away about the strength of my hand. My bet could be bluff or I might be calling on a draw or I could have the stone cold nutz. Even when I'm fairly certain of the line I intend to take from the beginning of the hand to the end, I still want to take a little time before I act to make sure I'm not overlooking any details, but also to maintain an even tempo that suggests neither strength or weakness to others. But sometimes I want to take a few seconds longer to give the appearance of trying to make a hard decision.
Notice that I said "a few seconds longer". The thing is not to let it become obvious. Once it becomes obvious that you are just putting on a show, whether it be for the cameras or for the crowd or the other players at the table, then you've taken too long. Just like watching a stage play or a movie, the act should seem natural. Once it becomes obvious that you are acting, it gets real old real quick. No one appreciates a bad actor. How many old horror flicks have you turned off half way through because you just couldn't stand the awful acting any longer?