I've got one too, for alto, although I still use the Rovner. The plate with four dots is supposed to be the freest-blowing, the one with two ridges across the plate is more for classical as it's supposed to be more restrained, and the one with two ridges along the plate is, er, well, somewere in between, maybe more 'focussed' or something, you'd have to read the Van Doren bumf for the full description (I think you got it right there Rhys, it is a bit high-flown and hilarious).
Personally, even though I don't use it any more (hey, maybe I'll give it another go), the different plates do make a bit of difference to the sound, but no matter which one you use you tend to end up sounding like you anyway - maybe it's a case of each plate's differing qualities allowing you to achieve 'your' sound more easily, and one of the three will be 'your' plate.
I also used the 'four dots' plate.