I use Waze as well, though not actively. I just do passive traffic reporting. I assume all iOS 6 users will be doing that when Waze is integrated into Maps. That has some serious potential, but I'll reserve my judgment after I use it for a bit.
Waze doesn't really do directions and ETAs very effectively. It is better for seeing traffic, construction, police traps, etc. It is also not a particularly pretty app. The mapping is pretty poor in it and it feels pretty cluttered. Hopefully with the iOS integration, it will run like a champ.
It's not integrated into iOS. The Maps app is merely using Waze mapping data.