ESPN reports that Harvin will see "meaningful snaps" in his first game. It'd be nice for the Seahawks to actually put a snap count on Harvin, but this is the cloak-and-dagger way of the NFL. It's also worth noting that Percy lobbied to return kicks, but he will not do so yet.
Harvin had hip surgery just before the preseason and the Seahawks haven't had a chance to use the player they acquired in exchange for a draft pick from the Vikings this past offseason. He's said all along that he wanted to play in this game and try to stick it to his former team, so he will get his chance.
The stats were certainly there for Harvin last season and he was leading the league by a wide margin in yards after catch prior to his season-ending injury last season. There are not many better at making plays in space than the University of Florida product.
Fantasy impact: It's not going to be easy start Harvin. He's more of a high-upside, high-risk play for owners. If you find yourself having a rough afternoon and need to swing for the fences in a PPR, he might be worth a start. Otherwise, he should be on most benches.