Perhaps just my opinion, but a camera body is pretty much the very last things of importance in photography. Brand is pretty much not relevant at all either.
Tom is a friend that I met just this last year during a meet-up. To this day, he's one of the most creative and inspirational wedding photographers I've worked with. I rank Tom as of the tops in my book.
His camera of choice is a Canon 40D. Why? Show me where his images lack and where there's a need to upgrade.
http://www.tomkblog.com/denver-wedding-photography-shelby-regan#
Penny Adams is a personal friend and local. She shoots mainly with a 20D.
http://adlerhouse.com/
I wish my work was more than just a hobby gone one step forward. They are true professionals working full time in this arena. I love referencing their work as it's truly inspirational in showing that the best upgrade anyone with camera can do is internal and essentially FREE. If you must buy something, my advice, make it a great piece of glass or a solid lighting system.
The D4 does look like a nice piece of gear though :gabe: