I did the JMT, north to south, July 14-25. This is something I've wanted to do all my life, but only got around to doing at age 44. As a healthy antidote to any overblown feeling of accomplishment, I met some young kids on the trail. Two 12-year-old twins from Wisconsin, hiking with their dad, are making their third attempt to set an age record for yo-yoing the JMT. The current age record is 17. I met them when we were all resupplying at MTR, and it was fun watching them divvy up their candy, etc. Later the same afternoon, I passed a woman and her small daughter along the south fork of San Joaquin. I didn't think much of it at the time (except to be surprised at someone hiking with a small child in a relatively remote region), but I learned later that afternoon that the girl was 6, and is trying to set an age record for the JMT. When they come to a significant creek crossing, her mother carries the pack across first, then goes back and carries her daughter across.
This was a heavy snow year, and a lot of PCTers have reported problems on the JMT section. A couple of PCTers were swept away at the south fork of the Kings in the first week of July, and banged up pretty badly. A lot of PCTers have resorted to skipping the JMT section, and then coming back to do it later. Unfortunately for my nerves, stories like these were bouncing up and down the trail, where they lost the accompanying information about when they actually happened. For the most part, there were no huge water or snow problems on my hike. The two crossings at Mono Creek were the hardest for me, but were not really too bad by the time I got to them. I don't use trekking poles, so I learned to anticipate the bigger crossings and pick up a couple of good, strong sticks well in advance of each one. Evolution Creek I crossed upstream in the swampy, safer area. The south fork of the Kings was absolutely inconsequential by the time I got to it.
The high passes in the south half of the JMT mostly just had a little snow, which was no big deal. The biggest problem was Muir Pass, which was very time-consuming to get through due to a large amount of snow, mixed with some white-water creeks. I brought a small tarp and no special-purpose rain clothing, although I had a spare trash-compactor bag that I could cut up for use as a poncho in an emergency. This turned out to be OK, although I was a little psychologically intimidated by a very intense evening hailstorm early on in the trip near Squaw Lake. I wasn't as well practiced in my tarping skills as I would have liked to be, and took a long time to get the tarp up.
Although it was early season, bugs were mostly pretty manageable. I hiked in long sleeves and long pants, and wore a head-net fairly often. 100% DEET helped in the evenings.
After some ... er ... spirited discussion on this site, I decided to up my amount of food from the 2100 cal/day that I normally eat on 3-day trips. I ended up packing in 43,000 cal, buying ~5,000 cal worth of meals at Tuolumne, Red's Meadows, and VVR, and dumping ~19,000 cal in dumpsters and hiker boxes, for a net calorie consumption of about 2,500 cal/day over 11.5 days. Since I completed the trip somewhat more quickly than my original estimate of 14 days, this meant that I ended up packing out a huge amount of food. I lost 4.5 lb of body weight.
My gear list was discussed here: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=33701 My base weight ended up being about 12.5 lbs.
I had seen quite a bit of the northern half of the JMT before, but the southern half was 100% new to me. My backpacking guru had waxed poetic about the beauty of Evolution Valley, but I honestly didn't see what was so special about it. For me the scenic highlights were Donahue Pass and especially the middle fork of the Kings: aspens, wildflowers, ferns, deer, and butterflies so thick they became a hazard to navigation. It was also a real rush to go over Forester Pass in high gear after having been thoroughly acclimatized by all the preceding 12,000-foot passes. I actually thought Forester Pass was more impressive than Whitney, where the view from the summit looked like something you'd see from an airplane. One of my goals for the trip had been to learn to identify a lot of the plants. I studied up using the Wenk guidebook and the Laws field guide. Ate some wild onions as trail nibbles, although I never really managed to get together a really good wild-veggie salad.
Had a lot of fun meeting the PCTers, who seemed like the coolest people ever. A ton of them were hanging out at VVR taking zero days after coming up through the southern Sierra.
As far as gear, the biggest thing I would strongly think about changing in the future is that I might want to switch from running shoes to sandals. I had a bunch of foot problems in the first half of the trip, all of which seemed to be related to the interface between my toes and the fronts of my close-toed shoes. I ran into a JMTer who was hiking in Chacos, and showed me how they could be adjusted to fit his feet exactly the way he wanted.
People on this site were very generous with their time in critiquing my gear list, suggesting how to dry lentils, and in lots of other ways. Many thanks!