I bought my girlfriend's directly off the Ugg Australia website - probably didnt get the best deal, but I had heard the stories about the fakes that were about and preffered to pay a little extra for piece of mind. They came within a week and she loved them! I paid about £190 for them, that was 3 years ago.
On this website there is a section entitled "Counterfeit Education" i.e how to spot the fakes!