I guess it depends on whether they're going to use the Irish Subsidiary in such a way that it allows other legal entities to reduce their corporation tax bill in higher rate locations.

The popular one at the moment being The Double Irish (http://en.wikipedia.org/wiki/Double_Irish_arrangement) which Google, Amazon and Starbucks have been using very successfully recently.

Not suggesting this is necessarily what Dropbox are going to do but it might enable something like this, should they wish to.