To add to what the others have said, from what I have gathered there is not much reason to cycle on and off creatine. While you will become habituated to its effects after a while, its still there doing its thing during exercises which use the creatine phopshate system.
In addition, creatine is showing promise in a host of other applications not related to exercise, such as cognitive functioning.
There is some theory out there relating to potential creatine transporter downregulation, so that, when intracellular creatine levels are very high, these transporters are downregulated, and absorption of more creatine is next to impossible.
It would make sense that, when intracellular levels drop, these transporters would appear again. I don’t know if this is something that happens relatively quickly (say, after a workout) or if intracellular levels have to be low for an extended period of time (such as when cycling off creatine.)
I’ve only seen blurbs of this, however, and I think from what studies are out there, none show this to be the case for the amount of time of the study.
But if anyone has any links to new research, please post 'em.
So, personally, until some clear and convincing evidence comes along that demonstrates greater increases in performance while following a specific cycling guideline, I just take it year round.