I'm not sure why I was so nervous, really. A simple color scheme change makes Gmail feel similar to Comcast (which probably means Comcast's redesign was meant to mimic Gmail), with a few minor improvements and a few minor annoyances. (And luckily, it turns out pretty much everything was going to one of my three auto-forward addresses.) I haven't yet played with their more advanced tools like threading, though. I think it was the right move.