In CLAY soil, looking for best method to set wood fence posts?
When I redid my fence 2 years ago, I went with PostMaster metal posts (http://contractors.masterhalco.com/Contract.nsf/woodpostmaster). They weren't substantially more than a good PT post at Home Depot. You can also easily wrap them with a picket so you don't see metal.

I dug the holes about 30" deep, then just drove the posts into the dirt til they were the right height - much easier than cutting them. You could put a couple inches of pea gravel in the hole, but I just did concrete. My hope is that even if I have to rebuild the fence in 20 years, I'll never have to replace the posts.