It'd be nice to be able to create a custom error message that says something like "Please try again later or contact this email address" when there is an error in alfresco. Currently it displays a full stack trace (well, in show details). Is it possible to customise/override this page?
Also, is it possible to get log4j to email logs to somewhere?
You can't do this out of the box but you could customise the SystemErrorTag class which is responsible for rendering the majority of the error page. Alternatively you could add your text directly to error.jsp.
To do the former suggestion change the definition of the systemError tag in WEB-INF/repo.tld to point to your implementation. You may well be able to package all of this in an AMP but I'm not sure if anyone has tried replacing a TLD file in an AMP, best thing is to give it a go!
Of course you could also replace the standard error.jsp using an AMP too.