Asked Alex about this (just type in "fare lock").

Her reply:

Alex: FareLock allows you to hold your reservation and fare for 72 hours or seven days, for a fee, and is available on Continental-operated flights only. If offered, you can purchase FareLock after you have selected your flights.

(No link offered)

This coming from the CO site (not preview, the official site).

I guess it's something in progress? I'm okay with it, as long as they keep the 24-hour cancellation period.