"Everyone says it is a great lens"?? Well, it has a few devotees who do rave about it. And they will take up arms against any criticism, but, they clearly have never used a real tack sharp prime. See http://www.birdsasart-blog.com/2011/03/14/which-is-the-best-under-1500-canon-intermediate-telephoto-lens-for-me/ where Art Morris says "At this point in my life, I would not consider a lens without IS so my old toy lens (= 400mm f/5.6L) is on the shelf (though it is likely that I could still use it effectively. Unless you wish to use a tripod all the time (except when doing flight photography), your choice is between the 100-400 IS and the 300 f/4 IS. It is a tough choice. Good luck making it "
Thanks for the link, AlanF, I hadn't seen that blog post. I have, however, looked over his site a number of times and there are a boatload of EXCELLENT shots taken with the 400 f/5.6.
I decided to pull the trigger and went ahead and ordered the 400 from the refurb page (thanks to Mt Spokane for posting the heads up). If for any reason it doesn't perform to my satisfaction, I'll probably wait for the mythical new 100-400 with the latest IS to be released, then consider selling both my beloved 70-300L and the 400 f/5.6.