In the studio: OSX Jaguar and Tiger on a G4 450 and G4 dual, respectively. At home: a G5 dual and a new G5 quad running Tiger; an iBook running OSX; and a Strawberry iMac running OSX Jaguar, which takes up nearly the entire hard drive. (My 8-year-old G3 is under the desk, still running like a top, but lately ignored.)