Along the same lines, are you doing anything special with munin to make it fast? We've had performance issues with the RRDs and graph generation that led us to pipe metrics to graphite with collectd.
We've had to split munin across three masters (by machine role) because the graphing job was just locking on IO. Munin 2.0 moved over to all-dynamic CGI graphing, but I haven't gotten the chance to play with it yet.
