Most significant signing: The team's most significant addition has been running back LeSean McCoy, who will become the cornerstone of the team's offense after arriving via trade. I'd consider Matt Cassel the Bills' second-most significant addition, because he could be their starting quarterback this season. But if we're going to narrow this down to a free-agent signing, it would have to be wide receiver Percy Harvin. If he can stay out of trouble in the locker room and stay healthy, Harvin has the upside to emerge as a valuable offensive weapon.
Most significant loss: This one has flown under the radar, but the Bills lost one of their better defensive starters last season in safety Da'Norris Searcy, who signed a four-year, $24 million deal with the Tennessee Titans that includes more than $10 million in guaranteed money. Pro Football Focus graded Searcy highly last season, his first as a full-time starter in the Bills' defense. As with the departure of Jairus Byrd last offseason, the Bills will need to find another player to step up. Duke Williams is the top option.
Biggest surprise: If we're to narrow this down to only the Bills' activity in free agency, their signing of Tyrod Taylor might qualify. He wasn't a name many connected to the Bills before this week, yet coach Rex Ryan appears to have every intention of making Taylor part of a three-way race at quarterback. Taylor could receive up to $7 million over two years if he emerges as the Bills' starter, according to a source, and he turned down a richer deal from the Denver Broncos to come to Buffalo. After trading for Cassel, I don't think many were expecting that sort of signing at quarterback.
What's next?: The Bills went into the offseason needing to address their tight ends and offensive line, and outside of their roll-the-dice signing of Richie Incognito, they haven't done that. In fact, the Bills have lost their top two tight ends from last season -- Scott Chandler and Lee Smith -- and missed out on signing top free-agent tackle Bryan Bulaga. Whether it's Charles Clay or a high draft pick, they're going to need to do something at tight end, given that position's importance in coordinator Greg Roman's offense.