In the spring I just use a tree to break my outline (check out Diesel77's pictures on the second page of the "What to wear" thread to see what I mean). When you pick a tree to lean against make sure it's as wide or wider than your shoulders if possible.

In the fall I use a portable blind, but that's because I fall hunt with a dog. I have a sack I put her in (with her head sticking out)and I sit with my legs pinning her down. The blind hides her fidgeting.

I’ve killed turkeys both ways, but I don’t put up with the bother of a blind unless I have to.