The software update won't do much for me, since I have a more straightforward HVAC system. What I'm *hoping* they've done is souped up their logic for "gosh, the sun is shining right on the thermostat, so maybe I shouldn't trust the temperature reading". Right now, I have my Nest programmed for the late afternoon to tweak the temperature so it doesn't drive the house into frigid temperatures.
Also interesting, if you look at the new base plate, they appear to have adopted a small amount of wiggle room in terms of the screw holes. This is a big deal if you want to get the thermostat installed truly level. (Losen the screws a bit, tweak, then tighten down again.) Can't do that on the 1st-gen Nest.