As I mentioned in a previous post, I don't have all my shields stacked up - I'm just running wires from the Arduino to the Ethernet shield, and out from there to the LCD shield, the buttons, and the RTC.  For the life of me, though, using this setup, I couldn't get the Ethernet shield to pick up an IP, and subsequently, nothing else would work in the sketch.  Finally, I figured out that I have to run connections from the Arduino ICSP header to the Ethernet shield, and then everything is good.  I was under the impression that the ICSP connections were just duplicating pins that I had already connected (10-13, power, ground), but apparently not.  One of these days when I have a bunch of time, I'll dig into what's really going on, but for now, it's enough to say that it's working.