A recent study shows that more and more people are now looking to search with long tail keywords. This has probably to do with lots of less relevant links making it to the top of competitive keywords thanks to SEO.
Keywords with 8+ words have had a 6% growth while those lesser than 5% have seen a decline in the volume of searches
One word : 24.32% (0%)
Two words : 23.55% (-1%)
Three words : 20.52% (-1%)
Four words : 13.69% (-1%)
Five words : 7.94% (1%)
Six words : 4.30% (2%)
Seven words : 2.33% (3%)
Eight and more : 3.35% (6%)
http://techcrunchies.com/average-length-of-google-search-keywords/