I have a private plate on my Ford Racing Puma W179(build number) FRP, a fair few others are on plates with FRP. Also see a fair few Focus RS's with RS or FRS in them.
As a marque, I see more Saabs with chav plates than any other, followed by Audi and BMW, although specific models such as BMW M and X variants attract chav plate usage more than other models.
Oldish Rolls Royces (Shadows and the like) always seem to have a 3x3 dateless plate on.
3x3 dateless plates look so much better than the current format. Unless the new ones actually make a decent word I really don't understand anyone paying for one.