I've done this trail from The horse center on Quince orchard road , all the way to the Potomac at Pennyfield lock. seems to be abut 10-15 miles total so far. It is a work in progress and new signs and blue blazes and trail head posts are springing up every couple of months. (this review is on 12-24-2015) It's pretty easy to follow, and you have to look around for the trail at each road crossing with the hardest to find being the Query mill/Esworthy road point, heading down stream. You actually have to hike up Esworthy road about 1/3 mile and the trail continues near a utility line. down a very steep hill, then back up a hill to the River road crossing. Which then deposits you at the blockhouse point series of trails. Great hike if you live in the area, as I do. it's only five minutes from my house.
This is a very nice trail. What is described here is less than half of the trail that stretches from Route 28 to River Road close to the Potomac River. There is parking at Route 28, Quince Orchard and River roads. Full description available at http://www.montgomeryparks.org/PPSD/ParkTrails/trails_MAPS/muddy-branch-greenway-trail.shtm
This trail is pretty decent if you want to go hiking on a trail where there's not a lot of people. The path is pretty narrow so keep that in mind. Also there is not really good parking around the trailhead we just parked on the side of the road.
Just did this trail today, 11/10/2012. Very nice. Definitely moderate ... A few nice climbs. I didn't do the entire trail only went about 3.5 miles in, As for directions, I parked on the grass on the side of query mill, the trail begins a few feet before the bridge. I circled for a while on Turkey Foot before parking on query mill. Saw a few bikers, runners and fellow hikers. Lots of birds and critters to see.