Depends... If I'm working on small sections I'm likely to use slows and quicks, or yit-tut-tahs, if I'm working on choreography I'm likely to use an 8 count. What method I use doesn't matter too much, but intonation and emphasis does, so I know where my accent, commas and periods are.
Similar: it depends on what I'm working on. But I generally only count during lessons or practice. On the social floor, the only time I count (not out loud!) is when I'm executing a figure that I haven't learned very well yet.