The newest lens in my small arsenal is the recently released Canon 16-35 f/2.8 II. Its bigger, badder, and more expensive than its predecessor. The Mark I was known for being a bit soft at the edge, so much so that some people have gone for the half-as-expensive 17-40 f/4 instead. The Mark II helps re-justify the 16-35's greater price tag. Of course, none of that really matters if you're shooting with a Canon 10/20/30D or Digital Rebel -- the 1.6x crop factor of those cameras cuts off all the fuzzy bits -- but lenses outlast the bodies they're attached to. One day I hope to have a full-frame camera for shooting architecture.
I was in a bit of a rush to get this lens because I want to break it in at Sea Otter this weekend. The wideness will be more useful for MTB shots and will also help me get some nice panoramas of Laguna Seca. It will also be useful for road shots where I'm standing really close to the action.
Rather than recommend the same course of action to others, I'll list the pros and cons I debated in choosing this rather extravagant purchase.
Pros: * f/2.8 is fast and you'll need if you are planning on shooting in the woods or in bad weather * better edge sharpness than the Mark I, though not applicable for 1.6x crop cameras * 1.6mm wider than the 17-40mm f/4L on a 1.6x crop camera