In a word...
Huge.
People are looking at the behavioral aspects of the move. Forget that garbage. He's not going to shoot up a snowbank (that actually makes sense in several contexts) or go over Niagara Falls in a barrel. He's going to get in there and play some crazy football. Partially to prove his detractors wrong, but mostly so he can earn some giant money next season when this one year contract is up.
So let's move on to the fantasy stuff. First of all, there's Lee Evans. He had last season's quietest 1000 yard season, with 1017 yards and 3 TDs. Amazingly, he did that with only 63 catches -- his 16.1 yd per catch average was 5th in the league among WRs with 1000+ rec yds. It was clear to every fantasy football owner, everybody in the stands of every Bills game and, somewhat surprisingly, the Bills management that he needed some help. Well now he has it. With Terrell Owens lining up on the other side, Lee Evans should be a fantasy monster. I'm certain that he'll beat last year's numbers in catches, rec yds and touchdowns. Get ready for it.
This signing is bad news for Josh Reed who was last year's WR2. He's pretty much out of a job. Sorry Josh, have your agent give the Titans a call. This bodes well for second-year man James Hardy though, an absolute speedster who finished with two receiving touchdowns despite catching only nine balls all year. There will be a time in every single game where the defense will be horrified to realize they don't have enough guys to cover Evans, Owens AND Hardy.
There's also the small matter of the quarterback who will be throwing to Evans and Owens, which would be Trent Edwards. Edwards didn't light the fantasy world on fire (2,699 yards, 11 TDs, 10 INT) last season, but a closer look at his stats shows that he has a bright future.
He finished the season with a QB rating of 85.4 which you have to admit isn't all that great. However, it was better than guys like Campbell, Flacco and Roethlisberger and I'm pretty sure those guys weren't on the waiver wire in your league. It's also only one point behind Eli Manning, McNabb and Cutler.
QB rating doesn't directly translate into fantasy value but it's a decent guide -- and you need a guide because Edwards only threw the ball 374 times last season. That's the lowest number of pass attempts of any QB with 2500+ passing yards last year. He completed those 374 attempts at a 65.5% clip, the sixth best completion percentage in the league. The Bills didn't ask Edwards to do much, but he did what he was asked to do very, very well. This season, they're going to ask him to do much, much more.
As a final thought, compare the "Fantasy Four" positions (QB, RB1, WR1, WR2) for the Bills and the Cowboys:
Dallas: Tony Romo-Marion Barber-Roy Williams-Patrick Crayton
Buffalo: Trent Edwards-Marshawn Lynch-Lee Evans-Terrell Owens
Taken as a group of four, which side gets the edge? Not as easy as it should be, is it?