I currently use the 100-400L with the 7D primarily for bird photography. Whilst it's a good combination for what I'm using it for, there are times when I wish I could zoom back further than the 100mm will allow, especially when out at sea and birds are coming in too close.
If I had the dough, I'd splash out on a 70-200 f2.8 for the extra versatility it would provide. To me it would be much more of an 'everyday' lens than the 100-400 is, even though it doesn't have the reach. From what I've heard it's a sharper lens than the 100-400, although as you can see, the 100-400 still takes a pretty reasonable shot.
