Edit: This forum posting mentions using 16GB Sandisk Class 4 (slower) cards with no problems: What to consider when choosing a memory card for Nikon D90? - Photography Stack Exchange
Again, do me a favour and read the
manual if you want to know what cards are will work best with the D90 or any other Nikon.
Its all there ! No need to rely on forum posts that rely on heresy, that forum link doesn't really say much at all, its just a bunch of noise consisting of pointless chatter of different people stating their personal experience based on no evidence of any degree of thorough testing.