score:7
Your bag will be checked all the way through, and you will not need to collect it at SFO.
If you are following the same path on the return journey, then when you check-in in Seoul they will "tag" your bag all the way to SNA (Orange County), however you WILL need to collect your bag in SFO, carry it through customs, and then give it back to the airline. Giving it back to them is a simple step given that it's already tagged - in SFO you simply turn left after you go through customs and you'll come to an area where they will scan the barcode on the tag, put it on a luggage belt, and you won't see it again until SNA!