I have 4.6 version of OpenACS running at a client site (ILO in Geneva) since April 2003 w/o any problems. If Jeff's committed version is based on a version I provided Mohan, then I am fairly confident that it is very stable.
Last week I downloaded the 5.0 alpha version and and installed ILO applications. For the moment all seems fine. I will have more information in the next couple of weeks as we test the applications more thoroughly. Just a reminder besides the core we use File-storage and FAQ.
