Siping has been used in the heavy truck industry for years and it is very effective at increasing tire life if it is done right. One problem that can and does occur is rock drills. This is where a small rock will stick in the siping and drill its way into the tread. If you run on dirt roads alot, especially ones built using blasted rock, this can become a real problem. I have seen brand new truck tires pickup three or four rock drills in a single trip, makes for alot tire patches. I would definitely run siped tires as long as I wasn't running on dirt roads for long periods at higher speeds, if you're commuting on dirt roads stay away from siped tires.
Good times.
Good times.