You don't need to look much further than horrendous drafting - Maybin, McCargo, etc. Bills threw away a lot of high end picks on those turkeys and JP Losman, etc, etc.
Turnarounds can happen fast in the NFL - see KC last year - but I would say three years of drafting right and having a good scheme and good coaches. Unfortunately we're behind the 8 ball on the draft front since we gave up so much for Watkins - a panic move. Although on the other hand, maybe we're not so far away as I thought and Watkins is the guy to put us over the top.