Qbs has reached a state where it's conveniently possible to build projects of the complexity of Qt Creator. Therefore it deserves a version number that reflects its usefulness to the public. To encourage you to use it for your own projects, we hereby present to you qbs 1.0.0.
Why should I use it?
Qbs takes care of your build environment. Build your project for different platforms in the same shell.
Build multiple configurations of your project in parallel.
Fast incremental builds. A speed comparision is here.
Qbs is supported in Qt Creator 2.8.
Qbs is not tied to the Qt version. That means switching the Qt version doesn't automatically switch your build tool version.
This is a question that arises very often. Though it would be possible to replace the current qmake-based build system of Qt with qbs, we still would need a configure script and our infamous syncqt. I don't see much gained from that. We're aiming somewhat higher and want to replace configure and syncqt as well. That's where qbs still lacks features. Also, bootstrapping qbs is not possible yet.