You mean logs of chat content (messages), right?
Privacy is everything, we do not log. Many of our users are using OpenPGP or OTR encryption, so it doesn’t make sense to log such messages. We store only information that is required to run the server. E.g. offline messages need to be stored somewhere as a matter of principle. Last but not least logging is probably in conflict with German/European law.
Privacy is one of the most important reasons for many users here in Germany not to use ICQ, MSN and all the others.
We do not audit either, though this can change.
Hmm, although, sometimes these logs can be helpful to the company to look for suspicious illegal activity if need be or to generally make an online log viewing service for it’s users if it wanted. Many things can be done with logs than them to be just ‘archived’.
One may want to implement XEP-0136 to make archive logs more useful.