Richard-
I'm using the Leica DCS, it's completely automated- it has a sensor to
position each block for facing but I prefer to use the coarse and fine feed
buttons on the touch pad to face the blocks. It throws paraffin around a a
bit as the disc rotates at  faster trimming speeds, but this is bothersome
only if you're a neat freak or cut a lot of CJD biopsies. I like it.
Jeff Silverman