This is my third pair of Uggs and they aren't cheap, so I figured I should find a way to clean them up. I've heard of people using vinegar and water but I was nervous about that because the dye on these is so dark. I used mild dish detergent (Dawn) and cold water. I dabbed the soap solution on the stained sections (not scrubbed) and left them to dry.
-waiting to dry-
You may have to repeat this process a few times because you can't tell if the stains are still there unless it is completely dry. I wouldn't say they are good as new but they are definitely good enough for another Winnipeg winter.
Make sure to treat them with protective spray once they are cleaned!