I've had good and bad horizontal ones. Some of my Ford examples would drip all over me no matter what I did. Like thescreensavers's G35, the G37 is canted just so it doesn't make a mess at all. The small block Chevy engines had vertical filters, dome down, but they were fairly well behaved, with a little caution. I'm not too concerned about orientation, provided it's not totally stupid, just as long as the filter is easily accessible without contorting oneself and without putting oneself in the path of spills, and keeping most hardware out of the path of oil spills.