DISQUS

Puppet is nice in theory. In practice we found it is quite unstable for big installations (~100 servers): there are multiple memory leak issues in both puppetmaster and puppet client, stability issues where both die from time to time and even file corruptions. These problems are being slowly fixed with each new release but right now using puppet for big installations is source of constant problems and wastes a lot of time of our sysops team. Unfortunately you don't notice these problems until you get many servers to manage; on smaller installations it seems to work without problems (or at least they happen less often). In our case number of servers we manage increased slowly so we felt into the trap and now rely on puppet too much so it is quite late to change.

If you start afresh I'd take a look on cfengine: it is not as flexible and nice as puppet but probably is more stable simply because it is more old. In the long run puppet will be probably ok too as it is being developed actively but right now it is in "beta" state.