Got my new (july/aug) issue today. About half the letters were about items in the previous (may/june) issue, half were either about older articles or undated. None of the published letters took issue with the way the circ issue was framed. If no critical letters appear in the next issue, I'd say there is some serious head-in-the-sand attitude going on! I can only hope they are saving up a bunch of letters to publish together (ideally with an apology or at least an explanation).
And to all of you who did receive acknowledgments from magazines: that's very cool. It's certainly not what most mags do with most letters.