I've noticed though, that some bands now tend towards a 2nd encore for those "special" nights where the chemistry is just right. I figured that these days, the first encore is simply a quick toilet break for the band.

I've been to some shows where the crowd didn't deserve an encore, yet the band came back anyhow - that's when it stands out to me as odd. And others (Sigur Ros springs to mind) where the atmosphere was electric and the crowd cheered ecstatically for 5-10 minutes, and the band didn't come back on; but i kind of respect that.