Jeeves: If you want to get into the ISP side of network engineering, make sure you read up on BGP, and become really familiar with it. It's the kind of thing that you only really learn on the job, but to get the job you're expected to know it.
When I was sitting in on interviews for senior network engineers, the amount of people that had acronyms up the wazoo written on their CV, only to have no clue on such things (for example :how many usable IP's in a /27) was staggering.
Other protocols and technologies to get familiar on would be OSPF, 802.1q, 802.1ad, STP (*shudder*), MST, radius, netflow, snmp, pppoe, and qos.
Also subscribe yourself to the NZNOG mail group to see some real life banter between the network engies of NZ.
I completely lucked out in my career path. I did a year 1st level tech support at the warehouse, went to the UK for a year and did nothing but got drunk, came back and landed a kind of 'apprentice' network engineer role, which I stayed in for 4 years and am now at another ISP in a similar role.
Sounds like you got lucky indeed! I just need a bit of luck! I'm all up on my material and would be able to answer most of those questions if was ever asked..
Do you get exposed to a large amount of equipment working for a Large ISP? I'd jump at the chance to get a role like that, would keep be busy and on my feet something which I love in a job!