We just did the OS route - went up this last Weds (11th) and summitted on Thurs morning (12th).
Weather - yes, thunderstorms did roll through - quick and pretty violent on Weds when we were going through the Meadows area. Sat out some of it in one of the caves in the boulder field. It had been predicted as early afternoon but came through earlier - I think closer to 10:30am - 11:00am. We talked to a couple guys at the Climber's Ranch afterwards that had been about 100 feet from the summit when the storms hit - they ditched everything metal and sat it out. The weather reports that we saw prior to the climb at the Climber's Ranch were fairly accurate.
I agree with the previous posts on the Climber's Ranch. I made reservations for last week about a month ago and they were wide open. However, the ranch was pretty much full every night when we got there. So, if you are planning on staying there, I would recommend going online ASAP. The ranch is pretty much as described with the addition that they have a great library there and also a (slow) computer if you can't get away from email. The other nice thing is that you can talk to others that have either just come down or have a lot of experience - one of our "bunkmates" was a guide for JHMG (Keith ?) who was pretty knowledgeable about the weather patterns and such. Now, the caveat, as Lionel notes is that you are in a cabin that houses 4 - 8 people. I never got much sleep (even wearing heavy duty earplugs) as the other individual that was sharing the room snored really loud. But, if you can get past that the cabins have a bathroom, there are showers, a cook area, sink area, nice folks and resident moose and elk that wander by on occasion. Plus, you can probably find some of the cooking gear that we left there on mistake! OOPS!
Here is a link to the webcam at the Climber's Ranch - you can sort of see the weather going through.http://www.jacksonholenet.com/webcams/c ... _ranch.php
As far as the campgrounds, I think the closest ones were Gros Ventre and Jenny Lake - Gros Ventre was not full but Jenny Lake was full every day that we went through. If you went early in the morning (say around 7:00am or so) you might be able to hover around if you saw people leaving and wanted to snag a campsite. Jenny Lake does not take reservations but I believe Gros Ventre does.
Have a great time!