I have a pair of 10-year-old Danner Sequoias (which I don't think are produced anymore). 800G thinsulate. I wear them every day in the fall and winter, until it gets REALLY cold. Then I switch to a newer pair (3 year-old) of Danner Pronghorns with 1600G.
I'm also wearing a pair of Danner workboots every day during the spring and summer. I can't kill these things (or ANY of these boots, for that matter).
Danners can be pricey, but like a lot of things, you get what you pay for.