Oh man they're UGLY. I only thought that yesterday, saw a really beautiful girl wearing those damned things and they sooooooooooo totally ruined her look, they're just gross. They're huge, fat, clumpy, unfeminine and just massively unflattering things - I'm sure they're comfortable but seriously, if you're that worried about comfort just wear your slippers and if it's raining, put plastic bags over them - you'll still look 100 times better than the fashion victim in their Uggs and you'll have saved a bunch of money in the process.
In winter, decent leather boots with proper heels are the most attractive and flattering look for women - by far. After that, there's every other kind of shoe, slippers in plastic bags, just plastic bags, plastic bags filled with dog product, then Uggs on the Universal Scale Of Attractive Female Footwear.
At one point I remember wanting them, but now I don't really like them. They would make me shorter and make my legs bigger than they already are, so no for me But who cares what others think? Wear them and hoewever you want them.