I own one and have it installed at a local venue so it's mostly used live.
Did some pre-production for a mates band on it the other week, recording everything pre-processing but creating a mix on the desk for shits and giggles in the control room. Truth is the desks eq, comps and in this instance, reverbs sounded great so I wound up recording the main outs for the band to take away that night.
I was able to route the captured tracks back through the corresponding desk channels so the processing was applied. However I wasn't able to re-capture each individual track post processing as I'd hoped hence resorting to capturing the left and right. It worked in this case but I've made a feature request on the presonus forum here...
http://forums.presonus.com/posts/list/20958.page
I'd still probably always resort to reaper for some of the more intricate things like gating and the odd "magic" plugin but for all the cpu strain I could avoid using desk processing I'm really impressed.