My experience with ceramic rims appears to be different to most others -- but mine are a bit worn (ie polished smooth) now. Mine are Mavic Crossmax, 1st gen (which I bought used).
I used them with standard pads initially which worked well in the dry but was very poor in wet weather (no brake power at all, quite scary). I then switched to Kool Stop green pads, which were not really any better.
I currently use some New-Old-Stock Avid (green) pads for ceramic [I was given] and these have been great, there is actually some brake power in the wet. I know these are no longer produced.
Ceramic rims don't really wear out, the surface is hard and doesn't form a wear dip like bare alu. The Ceramic pads are also very hard and wear very slowly, so the first set you buy will be the ones you'll use for a very long time. Don't cheap out.