WindFlyer:

SK has a special seating reserved for other *G - the very last row!

The system will go through and make seat assignments, starting with *G, but then the logic is to fill up from the back to the front! That said, once corrected, I tend to get lucky and get a seat block (which I've got to say is more than UA has managed for me!)

Things may have changed now with the 'snowflake' class. I know that I can pick seats out on our corporate booking site, but only for business and economy flex fares. I guess if you're on a cheapy, they will want to keep you in the food/drink free zone. Heaven help them if you were get a free glass of water!

Edit to add: Opps, misread your OP, this is for short haul only.