Hi marmot,
When I did the JMT in '07, I used the book - Guide to the John Muir Trail (Winnett/Morey) in my planning. It is a pretty good book about the trail.
Your best bet is to browse the wealth of journals here on TJ.
You will need a permit for the JMT. You can reserve a spot no earlier than 24 weeks before your departure. You can obtain one online at the following site: http://yosemite.org/wildpermit/default.htm or you can call them at the number listed on the site.
You specify “Whitney Portal” as your exit.
There used to be a site: http://www.nps.gov/yose/rptFullTrailheadDates.htm where you could see what has been booked - however that site does not appear to be up (maybe too early yet)
Another good site is: www.backpack45.com/johnmuirtrail.html
Enjoy!
-martin
OregonBeerMan