Based on HitWise data, searches using 4-8+ words increased last month. Searches containing 1-3 keywords fell or were flat. That is a significant shift for two reasons. Maybe more....but I'm only going to list two:
1. We're getting smarter as search consumers. The days of typing a URL into the search box to find the website at said URL are not entirely gone but, clearly, we are learning how to refine our searches by using more terms.
2. As more search terms are used the amount of keyword inventory increases. Do the math. 4! (24) contains 18 more combinations than 3! (6) and that's just for a single search. Multiply that difference by hundreds of millions and you've got an exponentially increasing level of keyword inventory.