I've been shooting football all season, mostly with a D700. But this weekend I really needed two bodies, so my backup was a D7000.
After halftime the battery in my D700 died (and I didn't realize there was a hot spare in the truck), so I stuck the 70-200mm on the D7000 and kept going. It worked, and having the extra reach was actually great, but it was frustrating as well. The D7000 just isn't a fast action camera. The AF is slower, and less reliable. The buffer is slower, and smaller. It made me miss shots.
The D7000 has a lot going for it; it's small and light, and the high ISO shots look great, but despite the fact that it's smaller and lighter, the deep, yet narrow, grip isn't as comfortable as the larger cameras for all day use. At least not for me. This isn't just the D7000 either, the D80 was the same way. And it's too slow. It sucks when a play is right in front of you, and suddenly nothing happens when you press the shutter button.
Nikon 70-200mm f/2.8G ED-IF AF-S VR Zoom Nikkor Lens for Nikon Digital SLR Cameras
Nikon 80-400mm f/4.5-5.6D ED Autofocus VR Zoom Nikkor Lens
Nikon D700 12.1MP FX-Format CMOS Digital SLR Camera with 3.0-Inch LCD (Body Only)
Nikon D7000 16.2MP DX-Format CMOS Digital SLR with 3.0-Inch LCD (Body Only)