If the NFL in 2011 goes by the rules it had in place for the 2010 league year, as many people expect it to, the Hawks will have to adhere to a funny little parity mechanism called the "Final Eight" rule. The rule is in place to severely limit the amount of unrestricted free agent signings a team in the top four of the playoffs and to somewhat limit the next four left as well, hence the final eight. Since the Hawks beat New Orleans to enter the quarterfinals of the NFL Playoffs, they fall into the second tier of four and theoretically will have to follow those rules. 

The rules state (from what I understand) that the Hawks may sign only one player to a contract that pays $4,925,000 or more. The good news for the Hawks is that they can still sign an unlimited amount of players with a first-year salary of less than $3,275,000 as long as their 2nd year totals don't increase more than 30%.

Additionally, teams 5-8 may also sign an unrestricted free agent if one of their unrestricted free agents signs elsewhere, so long as the newly signed player makes an equal or lesser amount than that departing player. So, in other words, if Matt Hasselbeck were to leave and sign elsewhere for say $7 Million a year, the Hawks would then be able to sign a new free agent within that budgetary range (thanks to jteckmann for the summary as well).

For a team that's trying to get younger and build through the draft, this rule isn't really a big deal, but it's something to keep in mind as many of us were hoping to make a big splash in free agency. However, with Matt Hasselbeck, Sean Locklear, Ray WIllis, Leroy Hill, Chris Spencer, Kelly Jennings, and Raheem Brock possibly leaving, along with several other lower level free agents as well, it could turn out to be a relative non-factor - we'll just have to wait and see which of the higher-profile and therefore higher-paid free agents will stick around.