One of the few reviewers of the lens with Nikon gear by the look of it. :-)
Ideally, I'd have liked to try it against the Nikon 80-400VR, but I couldn't find a dealer within 200 miles who had both. Indeed, finding a dealer in the UK who had it in stock, at much less than the retail price (£999.99 or around $1900.00 at the then exchange rate), was a problem.
After reading a couple of magazine reviews of both, I took a chance on the Sigma which was rated marginally better than the Nikon. A firm on eBay had new ones with full Sigma International Warranty at almost half UK price ($797.00 at today's exchange rate) and delivered it from Hong Kong within 4 days. So far (6 months), it's been reliable, which's something I've generally not found with Sigma lenses before.
It has good levels of sharpness across the aperture range, and produces detailed images from corner to corner. Contrast is excellent, and despite its size and weight, is well balanced on camera.
It's big and heavy, but then what do people expect? It's a cracking quality lens, with a great range. Just what I was looking for at the time.