I go back and forth on this one. On the one hand brining the
turkey does make the breast meat more juicy and tender but
on the other hand it waters down the taste. Harold McGee has
one of his occasional columns in the Dining section of today's
Times; http://www.nytimes.com/2008/11/12/dining/12curi.html
and he's a no-briner.

My latest method of attack on the holiday bird is flipping.
That's right, I flip the bird. ;-) I start it breast side
down in a 300 F oven for 30-45 minutes depending on size,
flip it one wing up and then the other wing up for about
20 minutes apiece, then increase the heat to 450 F flip it
breast side up and cook til done. The 450 degree oven browns
the bird nicely. Like McGee, I don't listen to that 160 F
nonsense. When the deepest part of the breast gets to 145
on the old thermal meter, that bird is done.

I've tried several different ways since we started getting
the free range, never frozen birds about 10 years ago, brine,
no brine, high heat fast, low heat slow, but flipping the
bird is the method I've finally settled on. I don't know how
it would work on the typical frozen Butterball but it works
out well on the birds we get.

--
Ken Fortenberry