I just took WAF for a very brief test drive after seeing ESR mention it on emacs-devel (trying to find an answer to a completely different emacs related issue). I really like how easy it is to install and try out a demo with it, and the manual isn't bad. I like the colored output and ascii-art progress bars. Nice touches.
It's all Python, which is both good and bad. The syntax isn't super intuitive (compared to basic make where you pretty much just list files and commands), being all python functions that set up and and get called by internals of the tool itself, but I guess once you get the hang of it that wouldn't be too bad. It also does more than just build. It handles detection of compilation tools, dependency tracking (yes it understands C/C++ preprocessing), and also does languages other than C/C++. If I had a new project I'd definitely give it a try.