9 out of 10 points and recommendedSharp, quick and quiet.Really needs a tripod for the sharpest shots ... but the foot is the weak link.
I've had mine on my camera with a Nikon 1.4 TC (for a 420 mm total) for the best part of a year. (There is no optical penalty with this TC - Lens combo!) It is an absolute joy for birding - although 2.8 would be a lot nicer - and way more expensive. It is also great for macro shots.reviewed March 9th, 2008 (purchased for $1,200)
I only gave it an 8 for construction quality, because the tripod collar and foot are simply flimsy. (I think the flex is in the collar rather than the foot.) I've wedged a cork into the foot to stabilize it, and this modification definitely creates far sharper images. Unfortunately, the Kirk or Really Right Stuff collars are clearly better fixes, but for now the cork will do.
In summary: except for the foot - this is an incredibly satisfying lens, and I would buy it again in a heartbeat!