We obviously try to get the drum sounds as good as possible while tracking... cause this is what we'll be listening to right up until the mix (which could be several work weeks later). When we do layer in samples, it's always as a supplement, not a replacement. Because we like to record in big, live rooms... and Tommy hits the drums (and cymbals) so hard, we'll mainly use a sample to enhance some hi freq. without bringing up the cymbal bleed and trigger gates on the live snare track. Same goes for kicks.