Online, I would never show. Your betting patterns are all you have as
tells online. Sometimes I like to think that length of decision matters, and I'm sure it does sometimes, however with the variables like connection speed and multi-tabling, you could be reading into something that is not there.
Live games; I try not to show, and lie often when talking about the cards I had. It is easy to get peer pressured into showing bluffs and sometimes I succumb to the pressure, however, I remember who I showed the bluff to, and keep a long memory.
One person in particular I have burned into my memory to bet at with the nuts next time we are 2-handed. Last game we played 2-weeks ago I bluffed him off 2-pair by representing the back door flush when I had nothing. He was very rattled and even mentioned it last night to another friend. If that impression is burned in his memory he is in line for paying me off again.