How long does the effect of Botox last?

I'm thinking about getting Botox, and I'm most curious about how long the effects last.
I heard that Botox isn't permanent, so the effects return after a certain period.
That is why there is also a lot of talk about needing to get Botox consistently to maintain the effects.
I would like to know, based on actual experience, how long the effects of Botox usually last.
I'm also curious how those of you who get Botox regularly schedule your intervals.