Well, technically I plan on using a tarptent.
It is kinda of hard to find a place to hang a hammock in the middle of the Majove desert (joshua trees maybe??) and than a week or two later at the top of the Sierras (abominable snowman??). Tentative planning on the PCT for April 2011.
Once I get North of the Lassen/Trinity Alps, using a hammock has crossed my mind. But, most of that (OR/WA) is unknown territory for me. So, best to just stick with a UL tarptent for the full thuhike.