Good points Jeff. I'll never let my 100-400 go because I get the reach and flexibility of a zoom. A great lens for the $$$. Sadly I Doubt Canon will ever update this lens with the new 200-400L that was supposed to be available later this year, prior to the disaster in Japan.
The new 200-400 has a built in 1.4x TC so you avoid all of the valid concerns Jeff noted about swapping TC's/lenses in the field.
It's going to be a great piece of glass for those who pony up.
That lens is expected to have a MSRP around 10k and sell for roughly $8,000.
As an aside Jeff is shooting a Nikon and currently (IMO) Nikon is handling high ISO noise better than Canon.
On the 7D I prefer to stay 400 or lower but find images clean up nicely all the way to 1600.
The 100-400 is a lens I wish Nikon made! Probably one of the best focal length per ounce packages to be found. Nikon makes a 80-400, but I'm not impressed. It uses the old "drive shaft" off the body to drive the auto focus, which is slow, as well as a battery hog. Were it a internal focus, they might have something. Hadn't seen Canon's 200-400L. The built in TC sounds like a cool idea!
Jeff
