Same issue for me too. On launch day it did work, and double/tripled up my bookmarks on my iOS devices after a few hours. I did all the things vbtrek did and even then, several hours later, iPhones and iPads all had hundreds of dupes. I shut off iCloud on my PC, turned off Bookmark synching on all my iOS devices to delete all the dupes, and turned them all back on to receive the correct bookmarks from my Mac.
Today I decided to try again as my PC's now have NO bookmarks as previously I was using MobileMe to keep everything in sync. The iCloud Control Panel says it is synching the bookmarks, but they never show up in my IE favorites.
I suspect Apple has killed the feature on their end pending a fix for the duplication issue.