I've always used Autotools for my personal C++ projects, but after hearing Casey talk about this Unity Build thing, I had to try it out for myself.
So, right now I have a small project, that is 1100 lines of code scattered into 10 files; a complete rebuild takes like 8 seconds, a very simple change, like modifying a stupid thing in only one cpp file only took half a second to complete, that was the best case but the most unreal scenario, with more real changes the build time took between 2 and 4 seconds.
Unity build, always, always took 2 seconds, which I thing is really great, and I even didn't have to change that much from my codebase to make it work.
I will post again in a few weeks when the project is getting bigger to see how the this evolves.