I've been wanting to replace this lens with the 24-70/f4. However, I'm not really sure if it's really worth.
On my way home yesterday, can't resist stopping to take a few snaps.
I made the switch and couldn't be happier- better handling of distortion at the wide end (but both are easy to fix in post), the newer IS, it is smaller, lighter, has the best macro ability of any lens outside of an actual macro lens, and it has a zoom lock switch so there is no zoom creep of any kind. The only down sides are the loss of the 71-105mm which doesn't bother me, and it is slightly more expensive.