Provide a curated blacklist that can be used and updated automatically
Yes, this is prob what will make or break the various extensions for this. Would adblock have been a hit without the lists? NO. Neither will any of the extensions that despam google search results. You really need this!
Dave Marseilles commented
I like the subscriptions idea.
Shane Halloran commented
I agree that this would be good.
One source you should use is blacklisted spam domains from Duck Duck Go (http://duckduckgo.com/press.2009.04.30.html). However there are 40mil+ of them, perhaps too much.
Douglas Barmore Jr commented
Like with adblock plus... where you subscribe to a filter list that is updated... would LOVE this!