I consider the Joyent (Ex-Sun guys) the gods of Unix based operating systems, just reading how they ported KVM from Linux -> Illumos displays their deep understanding of what is going on under the hood. Seriously if you want to be an above average Unix system administrator, consider learning and using Dtrace with Solaris/OpenIndiana as it will improve your troubleshooting skills immensely with *nix in general. I just wish it existed in GNU/Linux (yea,yea Oracle is trying this, but still very incomplete atm), and Linux based SystemTap just does not feel as awesome as Dtrace.