I haven't taken the exam yet, but have scheduled it a couple weeks out. I've been going through all of the GNS3Vault troubleshooting labs and can't say any of them are stumping me, and honestly am having a difficult time figuring out what to study for the exam anyhow. I have no intention of cramming ITIL or FCAPS info, though I'll at least read those chapters. Everything else is pretty much cake, well, except my old nemesis frame relay. I guess I need to brush up on that as well.
That said, the theory behind this exam is interesting, but flawed. At least IME. Maybe 5% of the time or less an issue turns out to be a config related one, and certainly it's never mysterious out of the blue config changes and now eigrp ASes are wrong, or VLANs are pruned, or IPV6 unicast routing has been turned off, etc. It's almost always something has died, and frequently it's not obvious. I just finished troubleshooting the death of a backup link that exemplifies this perfectly.
The backup link is back to back adtran netvanta ds3 boxes that bond 3 ds3s and then feed gige into two 7200 G2s. Basically ethernet P2P over bonded ds3. Well, the netvantas said all 3 ds3s were up and clean, and that the gige ports were up and error free. The routers said that the gige ports were up/up and no errors were incrementing. Looking at my syslog server, I could see that ospf was down, and could see that on one side of the link one of the 7200 gige ports had claimed that it was seeing a duplex mismatch earlier. Fiber-fed gige duplex mismatch. Ok. Well, anyhow - shut/no shut on the gige ints on the netvantas and 7200s didn't fix anything. Rebooting the netvantas did fix it.
Now. How do you teach someone to TS that? When everything insists there's no problem except a weird syslog message, what do you tell folks? "When in doubt reboot" is lousy troubleshooting (though it does work fairly often). OTOH, it would have saved me half an hour of fooling around just now.