Hey Hans,
Thanks for the feedback! Good news on your first request, yesterday VMware released Log Insight 1.5 TP2, which features AD authentication. If you want to read more about it check out my blog post here: http://sflanders.net/2013/09/11/announcing-vcenter-log-insight-1-5-tp2/. As for giving access to certain sources, the workaround today is to use a syslog aggregator and separate instances of Log Insight. Then you forward your logs to a Log Insight instance as appropriate.