There are four reasons why we don't support using JavaRebel in production at the moment:
Performance. JavaRebel at the moment has a performance impact that isn't noticeable in development, but would not be acceptable in production. We are talking about potentially several times slower.
Correctness. At the moment some of the really weird changes (not very likely to come up) may fail to update correctly. In development you can just redeploy, but in production this is again unacceptable.
Tooling. When you are updating production you need to be sure that the update will go through and a way to distribute it to the servers.
Licensing. At the moment the license charges per user. For production we would make a license per server or CPU.
We plan to address all of these issues by the end of the year and releasing a production version of JavaRebel. Until then production use is not supported. [ August 11, 2008: Message edited by: Jevgeni Kabanov ]
Considering that most server apps do not run in a sandbox it shouldn't make much of a difference. The target group at the moment does not include hosting providers, which may impose a stricter security policy.