The faulty ACU installations were done between June 15 and 21, 2011 for the Altima, and June 23 and 28 for the NV. NHTSA says that the unit "will not operate as designed and this issue may cause the air bags not to inflate in a crash ... This could increase the risk of injury." Um, yes. Yes it could.
Still, given some of the major Altima recalls Nissan has had to deal with in the past – hundreds of thousands in 2007 and 20,000 just a few weeks ago – this latest problem should be small potatoes to fix. Nissan will replace the ACUs free of charge starting on or around August 22. You can get more information from NHTSA here.