A friend loaned me a 400mm f2.8 L IS USM (I) lens -- the earlier version of the lens reviewed here. I loved the image quality from the lens, but the weight of the earlier lens limited the usefulness. Hand-holding and distance portraits were just too tough for any duration with the older version of this lens.
This new (II) version of the lens drops several pounts of weight. Mounted on a 5d mkII, hand-holding this lens works for minutes at a time and isn't a problem. I'm very happy with the purchase -- fulfilled by Samy's Camera in CA -- a plus for those that are in WA state. I was lucky and got one from an early batch in December 2011.
- Awesome image quality. Sharp over the full frame at f2.8. Non-existent distortion in all images I've looked at.
- Can hand hold it for useful periods of time.
- Extremely fast and accurate auto-focus.
- Great for distance portraits and sports.
- Much better lens cover design vs. older 'white whale' lenses -- much easier to remove and replace the lens cover. (see caveat below)
- New version of lens case. Easier to move lens in and out versus older style 'white whale' lens cases.
- Attracts lots of attention. Good for those that want it. It attracts the ladies (!). I'm neutral on this matter.
- Expensive. Make sure to pay with a credit card that offers 2%+ cash back.
- New style velcro lens cover can fall off if not pulled snug with the lens facing down. Expensive to replace, so pay attention.
- Attracts lots of attention. Bad for those that don't want it.
- This lens should also be great for gigapan style work -- haven't had a chance to try this yet.
- Some photo post-processing software doesn't recognize this lens yet, and offers to correct using the wrong lens profile (eg: 400mm f5.6). Just skip these correction operations -- isn't really needed for this lens anyway.
- Get a good mono-pod to go with this.
- Don't drop it ... and watch your surroundings.