There hasn't been any long term reports for the 2012 models, but the 2011 models were more or less free from rising blacks. I expect the 2012 models to be fine as well.
late edit: n/m, there hasn't really been any long term data for the 2011 models either. Cnet is the only site/person that seems to be tracking this. The Panasonic plasmas are the only ones that seem to have dropped and then leveled off, however they have only tested to the 2000-3000hr mark.