This is the default output of the munin load plugin.
I’ve patched it to add a permanent blue line indicating the number of cpu of the server. The resulted graph looks like this :

You can download the patched plugin here. It is tested with Linux and FreeBSD.

On some of freshly installed servers (Debian Etch), I encountered these error messages in /var/log/munin/munin-node.log:
Use of uninitialized value in eval {block} exit at /usr/sbin/munin-node line 456, <CHILD> line 8.
What a great error message
After digging into Google results, I found it was just a problem with host_name variable in the configuration. Default value is [...]