I ordered three pairs of Ugg's from Amazon this winter. Two pairs that I received were authentic and one pair were fake.  The fake Ugg's had the holographic tag, came in a box with a holographic sticker, and with packing and materials identical to the authentic Ugg's -- the only way I was able to tell the fakes were that they absolutely REEKED.  The boot itself smelled fine, like sheepskin, but the soles smelled VERY strongly of new plastic or chemicals. I could smell it before I'd even pulled them out of the box.  Real Ugg's do not have this smell.  Go to any fine department store and smell for yourself. If you receive Ugg's and the soles smell strongly of paint/chemicals/plastic... return them, they are not authentic.  If you are familiar with those foam rubber jigsaw puzzle pads they make for babies... it's that kind of smell.
At the time I purchased the boots, Amazon was not an authorized seller of Uggs (apparently they now are), however a number of the marketplace sellers on the site are.  If you visit Ugg's website, you can find a list of authorized sellers.  Unfortunately, as I discovered, several sellers on Amazon are using names very similar to authorized vendors but are not actually that vendor.  So be careful.  Some of these folks selling the fakes are still charging $180 for the classic tall.  You will not find authentic Ugg's on sale, reduced, or anything like that at any authorized site.  If you want real Ugg's be prepared to pay full price for them or end up with fakes.

The AUTHENTIC Ugg's I received were both from Shoe Central out of Ashland, Oregon -- they ARE an authorized dealer.  I love my Ugg's. I waterproofed them and that worked well for walking in heavy snow.  My toes were toasty warm.  Very comfortable.  I'm very happy!