It appears my Mint system is using NTP, but the reason I'm even thinking of this is that my system clock seems to be drifting.
The Mint User's Guide (still Mint 11 at the main site) has no mention of NTP, nor of "Network Time," the vague label used in the Date and Time settings. Dumbing down the interface by labeling what I suspect is NTP as "Network Time" is not helpful, especially if it's not documented. Someone who understands networking is left wondering if this is NTP. Someone who doesn't understand networking will have no clue what the "Network Time" switch is for:
Now I have to dig into the configuration files if it turns out I care enough.