Stealth Gate Announcements at Seatac C2 gates
 

If you're taking Horizon flights out of the C2F-K gates at Seatac be aware
that they often don't announce the boarding of the flights. They just
sort of magically happen. 3 weekends in a row I'm told while standing
there (different C2 gates each weekend) that you have to watch the
reader board, the "experienced" crowd, go up to the counter occasionally
to find out if boarding is actually occurring. But given my other experiences
with Horizon to date, this half-*ssed approach is how they seem to run
all aspects of the so-called "airline".

I fly through Seattle often and the "C2" gates are no different than any other "commuter" terminal at a hub airport. Have you ever been to SLC or IAH and experienced Delta Connection or Continental Express? It's exactly the same. There's a high concentration of gates in a relatively small area. Many times two flights will be simultaneously boarding from the same podium. It can be confusing but the advice that you were given to "watch the boards" is correct. They will have the most up to date gate assignment for your flight and let you know when boarding begins. Horizon always announces the boarding of each flight on the PA but since there are so many gates in that area the announcement is very localized and can only be heard in the immediate gate area. If they have stragglers I've even heard them shout out names without the use of the PA.

Why would you wanna look at the boards? Your boarding card should tell you exactly when boarding starts; that's the easiest thing to do. I mean if boarding starts at 2 and you get there at 12, then you would know when to be at the gate should you decide to grab a bite or somethin. You can check the board for gate changes, or if you wanna confirm the gate is the same, just ask an agent. They have to make some sort of announcement, even if they have to yell, I can't imagine running to a flight board and then running back just to get on the plane.

At Sea-Tac the board listing all of the horizon flights is centrally located within the gate areas. There's no "running back and forth" as you suggest. Because they are commuter flights gate changes do occur so it is a good idea to double check the departure board which is updated in nearly real time. Of course there are always employees at the gates who will tell you if you're boarding the correct flight.

Listen very carefully
 

even if they have to yell

In travelling to one airport near my home that's pretty-much how it's done. My "drill" goes something like this: You find the gate. Then you locate the gate agent(s) and try to remember what they look like. Watch for "switching-up" of staff. The object is to be within hearing distance of the gate agent when the boarding announcement is made. One has to keep in mind aircraft noise may significantly drown-out the announcement. So the closer you can get, the better (as long as you don't wind-up exchanging phone numbers!) Getting close may be difficult to accomplish during holiday periods. Unlike mainline flights the sight of people lining-up at the boarding door can't be relied on because you can't be sure, just based on sight, what flight is being boarded. Since the airport I speak of here is an Essential Air Service city, a crowd of much more than 8 to 10 people at the boarding door means it's NOT my city.

PHX is right, I used to remember the America West gate area in Phoenix.

Was that before or after T4 was built? Currently the gate configuration for America West...um, US Airways Express flights is more like the mainline gates. They are separated by quite a bit of distance and with the exception of one gate that they only use for the Q200 flights to Flagstaff and Yuma (no jetway) they never board more than one flight at each gate.