The thing about OpenStack is that it has been under really heavy development for the past two years. Two years ago the product was buggy as hell. But they've made a series of 6-monthly releases since then. Each one of which offered substantial improvements. Its now pretty good and stable. There is really a incredible support for it. I heard of numbers of around 2000 developers so each release really is substantially better than the previous.
Now that it is basically stable, it will likely get real traction with users and there are big private deployments already. The Australian NeCTAR project will roll-out 30,000 cores by the end of 2014. CERN is looking at a huge deployment of over 100,000 CPUs.