The trail is shaded for a good portion of it, making it pleasant to ride throughout the summer and at about anytime of the day. The trail is fairly wide through many portions, well buffed, and a grade that isn't too bad for climbing, but a blast descending.
Presently there is a river project (Kerns I think, pictured here) that is ripping up a portion of the mountain and interrupts the trail at about 1.6 miles. Right now it is impassable, so Mueller is unfortunately a very short ride right now, but normally it goes a lot further until it hits the big rock and bench and then continues on to Rudy's Flat. Still, if you're in the area it is well worth the quick ride, and a couple times up and back would still make for a decent ride.
UPDATE 10/2011: I hear that you can now ride through the construction area and keep going on the trail again.
UPDATE 10/2011: I hear that you can now ride through the construction area and keep going on the trail again.