I've always been a proponent of in body IS and here why-

Advancements in the technology are bound to occur from time to time, and as that happens, you will need to buy the same lens over again if you want to take advantage of the new technologies.

http://www.canon.com/news/2009/jul22e.html

Just think if I just went out and bought a brand new 70-200/2.8 L IS USM lens and then read that article? I'd be seeing if I could return it and wait for the new lens to come out.

There has always been a saying I've heard over and over- Bodies come and go, but lenses are a lifetime investment. Not true anymore w/ in lens IS systems. If I'm already bound to replace bodies (my current schedule is a new body approx. every 3yrs), with in body systems I'm already going to be getting the latest and greatest technology, and I can happily keep shooting with my old glass.

Just my $0.02

BM