How about doing what some of the other cloud sites do - accept "~" as a non-breaking space? So if I do a word cloud on:

apples bananas big~carrots damsons

it knows that "big carrots" should be kept together as a phrase. For what feels like a fairly ordinary thing for the user to want to do (keep some phrases together), it would be a lot easier for the user than having to use API, manual edit tags, etc.

Great product. You're a star. Keep it up!