I've been playing about with MRTG today, and found out that adding MRTG graphs to the Hobbit set of graphs was a very simple task. Since this is probably something that others can use, I've written up a short description of how to do it: http://www.hswn.dk/hobbit/help/hobbit-mrtg.html
The short story is that you can configure MRTG so that it stores its datafiles in RRDtool format directly into the directory where Hobbit looks for all of the other RRD files for a host. So with a "mrtg" entry in the hobbitgraph.cfg file and an extra entry for "mrtg" in hobbitserver.cfg's GRAPHS setting, I've got the MRTG graphs showing up as normal Hobbit graphs on the "trends" page:
http://www.hswn.dk/hobbit-cgi/bb-hostsvc.sh?HOSTSVC=fenris,hswn,dk.trends&IP... (a bit down that page, 3rd and 4th last graphs)
The detailed view is here:
http://www.hswn.dk/hobbit-cgi/hobbitgraph.sh?host=fenris.hswn.dk&service=mrt...
I did make one simple tweak to the Hobbit code for this - hobbitgraph normally bundles graphs into bunches of 5, which doesn't work well for the MRTG graphs. So I made the "5" configurable so I could get one graph per network interface.
I think it's neat :-)
Henrik