In order for a continuous integration system to be effective, it needs to be actually working.
I.e. bug-free. I.e. it needs to be continually tested, I guess.
We've been using Buildbot and have been extremely unhappy with it. A single little piece of this twisted monster, the GitPoller plug-in, is messing up the whole set-up.
When it stops, sorry, no more changes, and hence no more builds. And the damn thing is so badly written that it does stop. At first it used to stop when a branch with a specific name would show up in the tree. We fixed it. Then it turned out that it also stops when a few attempts to reach github have failed. We've fixed that too. Why it doesn't work now, I don't want to know.