A friend and I decided to do an overnight hike of this loop. The trail guide suggests taking the loop counter-clockwise, but since we wanted to camp at Sapphire Lake, we decided to take it clockwise. Be warned: If you go clockwise, the way up is VERY strenuous. We are by no means experts, but we're both pretty healthy guys in our early twenties, and we were exhausted when we finally reached Sapphire lake.
We got a late start hiking (about 5:30) and didn't arrive at Sapphire Lake until about 9:30, so we had to set up camp in the dark... So you'll definitely want to give yourself ample time.
The hike itself is gorgeous, once you get high enough up for the scenery. Going through the mountain pass as we neared Sapphire Lake, there was still snow on the ground in mid-August. Sapphire lake was really gorgeous, and we camped at an amazing site right on the lake. Although we were both totally exhausted, it was definitely worth the effort.
We left on a Friday, and didn't see a single other person on the trail until our way down the next day, when we saw about 20-25 other hikers and people on horseback.
All in all, a very difficult, yet very rewarding hike.