quicktime is significantly slower (start up and some glitches regarding replay speed while checking mail, and looks like you can´t replay mpeg vdeos (works fine under OS 9, but for all one i tried under OS X not; he, but´s BETA =8))
Image Processing (tiffany3), creation of vector/bitmap art with create is at least at the same speed as under OS 9; networking is really fast; responsivness of the gui is totally cool (okay I don´t run 257 apps at the same time <- my iBook has only 96 Mb Ram)
Os X resides on its own partition (approx. 1Gb); All PDF related things are really MARVELLOUS !!
Hope to get a c-compiler running; looking for X-server; like to install te-tex; but i´m happy with the whole thing =8)