Just wanted to report in with my experience on this on a recent flight to Kamloops -- both planes were nearly half empty, and my refund was promptly credited to my card only a week or so after I called. You *do* have to call -- or fill out a form online -- and they could make that information slightly easier to find. However, once I sat through the phone queue, it was all handled very efficiently. Once again, thumbs up to Alaska for implementing such a sensible, respectful and much-needed policy.
Oh, and remember how I wished that FAs would just hand out seat extensions as you board? On Horizon (or at least these flights anyway) they do just that. They were just sitting on a ledge as you board, easy for a passenger to take or a FA to grab one and hand it to you.
All in all, I was very impressed with Horizon, which I don't normally fly. However, it struck me that pretty much 90% of the people on board were uncomfortable in the teeny tiny seats (and I mean people of standard size), which makes me wonder how long they can really get away with such small seats.