I installed the preview for update 3 for WP8, and I gotta say, Driving Mode has been a hit with all of my friends and family that have gotten an auto reply.
"What app is that?" they ask, only to be disappointed that it's not an app, but built into the device. I'm sure Apple and Google will implement it soon, but it's nice that it's generating curiosity.
My parents both have Windows Phones (920 and 925) but I don't feel comfortable voiding their warranties by installing it, but they are definitely looking forward to getting that feature once it's available.
Those of you who have Driving Mode enabled, what say you? Do you like it/are people curious about it? I love it. Keeps me safe.