Washing machine method seems to be the most recommended method for the white UBs. If you google "how to clean white ultra boosts" there are several sites that have posted tutorials. Complex did a breakdown on it, they also did a breakdown on flyknits which you can't put in the washing machine, but I bet the flyknit cleaning method would also work for the UBs. Also, if you go back through this thread there are people talking about cleaning their UBs with various methods and various levels of success.
FYI the tide pen method I've heard can have mixed results. Sometimes it works, other times I've heard it just spreading the dirt around and almost making it look worse.
Next month I'm taking a bunch of pairs of shoes into the Jason Markk store out here to get em cleaned professionally. Will post before and after pics.