From The Economist:
California has been worrying about “runaway production” since 1998, when Canada began luring producers and their crews away from Los Angeles with tax breaks. Other places followed, and all but seven American states and territories and 24 other countries now offer, or are preparing to offer, rebates, grants or tax credits that cut 20%, 30% or even 40% of the cost of shooting a movie.
I'm convinced that some day this battle over film subsidies will turn into a big trade dispute (well, I guess I should say bigger, as there has already been a Section 301 petition, which was rejected.) I'm not sure when, though. More here and here.