Here's a nice chart from Toyota:
Notice that at the very worst, NOX is 20% higher than the stock tune, which is nothing to worry about. Conceivably, since we're all driving with a light foot we're probably releasing fewer total gases than the average driver despite the 20% lean-burn NOX increase. Also notice that if you go even leaner, NOX starts to come back down to stock levels.
GM's ECUs have a "lean cruise" mode, but it's disabled in all of their US cars to comply with US law. If you multiply that 20% NOX increase out to every Escalade, Yukon, Navigator, you can see why it wouldn't be a great thing in crowded cities. However, I'm not going to let anyone make me feel bad because my modified 2.2L might be producing almost as much NOX as their stock 3.0L.