I wash first, then shave. Every two to three days I use a scrub, then wash, then shave. The way I figure it, washing after shaving is like waxing your car before you wash it. To me, it doesn't make sense. The only time I wash after shaving is if I'm using Men-u cleanser as a toner (though I would still wash before shaving too).
Here's a good little blurb from Men Essentials on the matter.