I borrowed the 500/4 from Canon Professional Services when I had a situation which required that lens. I don't have many such situations -- but man, I wish I did. That is one sweet, sweet piece of glass. Focus is very quick, tracking is excellent, the viewfinder images is bright, and it's not really all that heavy compared to a 400/2.8 or a 600/4.
I am not a wildlife shooter, so I have no idea how well it would work for birds, etc., but for news photography, it is one nice lens.
When my spouse told me to buy the tripod I always wanted, I did hesitate -- for about 5 minutes.
Good luck.