Just a quick look at the HBT wiki on lagering yielded some interesting charts:
These are all graphs of different lager fermentation schedules, and the effect that different temperature regimens have on diacetyl concentration.
Although the article seems to suggest that the (C) and (D) regimens are better suited for homebrewers, from what I've come across in the forums, the majority of people are using a diacetyl rest, illustrated in (F).
It's interesting to note that all 6 of these regimens appear to result in reduction of diacetyl to about the same level. It's also worth noting that in the examples where temperature is increased briefly (as in a diacetyl rest), once the diacetyl has been sufficiently reduced, there is no need for a gradual cooling of temperature - you can "crash cool" to lagering temperatures without having to worry about shocking the yeast, since they've already done their job.
A number of people have touched on these points, but for me, it was nice to see in a graphical format.