We don't own one, but some friends that do say the front loads are not up to the task for cleaning dirty cloths.  Front loads probably work fine for city folks that are far removed from the real world.  My friends say they often have to run the work cloths through twice.  They think it is because the front loads do not use enough water to get the job done the first time.

Edit:  Wow...Looks like I'm in the minority on this one.  My friend's had the problems about four years ago.  Maybe the front loads have had significant improvements since then.  Still, with the volume of dirt that gets caked on some cloths, it would seem there would be limits to the water use efficiency gained with a front load.  The nature of the stain and the volume of substance to be removed are probably two different issues here.

Sometimes I scrape off what I can and spray the cloths with a power washer before attempting to put them in our washing machine which is still a top load.