I'm with the "let humans play it" crowd. Now, the are other ways to humanizing a piece with absolute on the spot timing (dynamics, arrangement, etc.) I think it may serve you better to humanize it that way then worrying about timing.
I think if you write it, so that it is off (ie: syncopation by anticipation and duration) in the first place, there wouldn't be a need to skew it afterwards.
Most often, the instruments in isolation are off-beat (if written that way), but hearing them altogether makes for a nice glue effect. There's the issue of counting correctly; however, it can be done.
What you don't wanna do is if/when you're composing is place a human behind the instrument because there's no way of knowing if something is playable. Likewise, if you're playing a part yourself and can't do it like you hear it, maybe someone else can and that person will tell you.