According to the fine fellows at ProFootballFocus.com - who are always ready and willing to toss praise towards a Buffalo Bills player that deserves it (and this is true of every other NFL team, by the way) - have done some interesting work to tangibly identify the inherent awesome of Fred Jackson.
PFF's latest statistical foray delved into a running back's elusiveness. Without getting into the nitty gritty - you really should read the entire article, anyway - the idea was to blend forced missed tackles and yards after contact into one rating. The result wouldn't necessarily be a list of the league's most productive runners last year, but the toughest to bring down.
Jackson's well-rounded game and shiftiness in the open field made him the NFL's second most elusive runner last season. Though he trailed Tampa Bay rookie LeGarrette Blount by a considerable margin, Jackson gets props from the guys at PFF for his consistency, his running/receiving skills, and his much improved pass protection (which did not factor into this study).
It's also worth checking out the article to see how well Marshawn Lynch fared in some of the categories, as well.