The Mint update program, not through apt-get update in the terminal, but the GUI one.... The Update Manager (phew! Got that one!) - will it be the source for the 17.1 update eventually or will it be something that I'll need to compile the kernel or boot from an ISO for?

As a part of the installation process, the Update manager will be installed. In the Mate version of Mint 17, it is shown as a small shield down in the bottom right corner of the screen near the clock. On the first usage, it will probably indicate that there is only one update available, but as soon as you tell it to update, it will begin the process, and install quite a few updates. After that it will not install them automatically, but will wait for you to choose to install updates. You will be given a chance to review the updates before installing, and choose all or only part. I usually just allow it to install all of the updates suggested - mostly, because the explanation of what any particular update is supposed to do is not adequate for me to understand.

Thanks for that LittleJoe5, I'm learning

No, you will not have to do anything special to upgrade to 17.1 - it will be automatic through the Update Manager.
http://blog.linuxmint.com/?p=2714

Actually, something must be done, but it's not much. With the new Update Manager, 'Update to 17.1' will appear in a menu (I can't tell you which one since it no longer appears for me, for reasons that follow). Selecting that item displays that one update. Immediately refresh to upgrade other packages. Once upgraded, and no longer on Mint 17, the menu item 'Update to 17.1' is no longer displayed.

You are absolutely right, Mik3e - and thanks for the tip.
I assumed that it would be obvious, and since I didn't see it I assumed that it had not yet been released. But there it is hidden in the EDIT menu in the Update Manager, for some strange reason...
(It doesn't really matter to me, personally, since I did a fresh install of Mint 17.1 on a different hard drive.)