http://www.davidnaylor.co.uk/google-analytics-short-taillong-tail-segmentation.html

I was just pulled into a conversation with Paul and James about developing a report of some kind in Google Analytics which segments short tail (1-2 words long) and long tail traffic (3 words or more). The advantage being you can then compare them and use it to estimate the amount of long tail gains you would get from going after a short tail keyword.