What are Nightly Builds?
Nightly builds are builds which are built and published automatically every night without any additional testing from JetBrains' side. Only our internal automated tests are passed.
You can try it at your own risk and post your feedback (as for EAP builds - into the newsgroup/forum and JIRA).
However, if someone tried a nightly build and reported us a problem which is critical, we add corresponding notes to the builds table. Also after some period of testing (e.g. 1 day) if there were no critical problems reported/found, we've add Stable mark for the build.