meh luxury tax is if i understand it correctly (im not a huge sports geek with laws and the like) is when you go over a certain amount. Then the government taxes you a dollar for every dollar over, essentially 1:1. Teams have gone over it before but very few like too and they tend to be Huge franchises like the celts, knicks, and lakers. a small market team like OKC would never want to. Heres the wikipedia explanation which is pretty clear.

While the soft cap allows teams to exceed the salary cap indefinitely by re-signing their own players using the "Larry Bird" family of exceptions, there are consequences for exceeding the cap by large amounts. A luxury tax payment is required of teams whose payroll exceeds a certain "tax level," determined by a complicated formula, and teams exceeding it are punished by being forced to pay one dollar to the League for each dollar by which their payroll exceeds the tax level.
While most NBA teams hold contracts valued in excess of the salary cap, few teams have payrolls at luxury tax levels. The tax threshold in 2005–06 was $61.7 million dollars. In 2005–06, the New York Knicks' payroll was $124 million, putting them $74.5 million above the salary cap, and $62.3 million above the tax line, which Knicks owner James Dolan paid to the league. Tax revenues are normally redistributed evenly among non-tax-paying teams, so there is often a several-million-dollar incentive to owners not to pay the luxury tax.
The luxury tax level for the 2008–09 season was $71.15 millon.[2] For the 2009–10 season, the luxury tax level was set at $69.92 million.[3] The luxury tax level for the 2010–11 NBA season was $70,307,000.
The 2011 CBA instituted major changes to the luxury tax regime. The dollar-for-dollar tax provisions of the previous CBA remain in effect through the 2012–13 season. Starting in 2013–14, the tax changes to an incremental system. Tax will be assessed at different levels based on the amount that a team is over the luxury tax threshold. The scheme is not cumulative—each level of tax applies only to amounts over that level's threshold. For example, a team that is $8 million over the tax threshold will pay $1.50 for each of its first $5 million over the tax threshold, and $1.75 per dollar for the remaining $3 million. In addition, "repeat offenders", subject to additional penalties, are defined as teams that paid tax in four of the five previous seasons. As in the previous CBA, the tax revenue is divided among teams with lower payrolls.[15] However, under the new scheme, no more than 50% of the total tax revenue can go exclusively to teams that did not go over the cap; the use of the remaining 50% has not been specified in the new agreement.[6]