the loop via the 5-mile long four mile trail to glacier point, and via the panorama trail to the nevada falls and down to happy isles was one of my favorite yosemite trail runs last year. yesterday i did the same loop again, but this time i hopped off the valley shuttle at stop #7 (camp 4); from there it's only 6 minutes to the trailhead, and you also have the opportunity to cross swinging bridge (simply take the bike path). once again, this run was just stunning, at some of the vistas you cannot help but grin from ear to ear because everything is so perfect. it took me 1:14 to get to the glacier point overlook, and the view from there is just breathtaking, in particular if you just ran up from down there and in fact are a little short on breath... there are drinking fountains at glacier point, so you can refill your bottle there (there also is a shop, so if you take money with you, you can get snacks and drinks).
from glacier point, follow panorama trail for a perfect downhill run to illilouette falls, along the way you can see a silhouette of half dome that most people don't have in mind when they remember it, you can see it sideways and suddenly it looks much steeper than usual. after you reach the falls, there is a little bit of climbing until you descend towards nevada falls. make sure to visit nevada falls, even if you are running down john muir trail, the falls are only 2 minutes from where you get onto john muir trail. i chose to run down john muir because the mist trail would have been much too crowded on this perfect weekend, and it is too narrow to easily pass people. the final stretch of the trail is very crowded, because everybody has to take it, but it is faily wide so it's not too hard to pass people. in the end it was 2:55 of running to upper pines campground (starting at camp 4), and the total elevation gain/loss was 1250m/4100ft.
this run is approximately 15 miles, so it really is not all that long. if you like running and are in yosemite, do it. you'll love it. the initial climb up to glacier point is long and hard, but it is runnable all the way to the top and the effort is well worth it.