It certainly wasn't the news fantasy owners were hoping for – Fred Jackson is signing with the Seattle Seahawks. It's a one-year deal, Adam Schefter first reported the signing.
Jackson met with the Seahawks on September 1, but speculation of a deal was quickly shot down by head coach Pete Carroll, saying it was "not a signing". If it was just a workout and physical, it appears Jackson passed with flying colors. Jackson is of course familiar with Marshawn Lynch, the two grew close when Lynch was with the Buffalo Bills and this is definitely a move that will make "Beast Mode" happy.
From a real-life perspective, it's a very nice pickup for a team that was looking at having Christine Michael as it's backup to start the season. Now they acquire a running back who can play a variety of roles, picking up short yards, working on passing downs and being a workhorse if Lynch was to suffer a serious injury.
Lynch is still going to be the featured back, really taking away any hope fantasy owners had for Jackson to land in a place where he could gain fantasy value. This move is a pure real-life benefit for Seattle, nullifying most of the fantasy upside. The only thing putting Jackson on any fantasy radar is as a handcuff to Lynch, who becomes worthwhile if Lynch misses a chunk of games.