Vanek, like Matt Moulson, can be an unrestricted free agent after this season. He was in the final season of a 6 year, $50 million contract with the Sabres and carries a 7.14m cap hit ($6.4m salary in 2013-14).
Vanek was the fifth overall pick in 2003; among his draft mates only Eric Staal (271) has more goals and only Staal and Ryan Getzlaf have more points. He has led the NHL in +/- (+47 in 2006-07) and in power play goals (20 in 2008-09). Since the Sabres has played two more games than the Isles, Vanek could play as many as 84 games this season.
Vanek, who will turn 30 on January 19th (what a great birthday!) has played in North America since he was 15; he played two seasons with the University of Minnesota. He is 5th in Sabres history in goals and is 10th in points. Vanek also is the all-time Sabres leader in shootout goals; he set the team record when he beat the Islanders in the final game of the regular season last April -- so in a way he was responsible for the Isles/Penguins series that resulted.
Vanek had 4 goals and 5 assists in 13 games with Buffalo this season, including a power play goal in Buffalo's shootout win over the Isles on October 15th.
The Vanek for Moulson (and 2 picks) deal is arguably the biggest trade ever made by Garth Snow, particularly if you are looking at trades with established NHLers going in both directions. The only other in-season trade you might say was bigger is the acquisition of Ryan Smyth in 2007, but none of the players the Isles dealt away were established (and none have ever developed into established players).