Hi HAF,
I've flown SFO-ICN-SIN each summer for the past 3 years and have to say that these flights are the easiest, most relaxing and highlight of my trip... all in Y class! Much more enjoyable than my UA flights from IAD-SFO to connect to SQ 15/16, even in Economy Plus.
I've noticed that the loads for SFO-ICN have been light (may be 50%) the past 2 years... last summer I had an entire row (3 seats together in SQ's 77W 3-3-3 configuration) for myself. May be due to the poor economy? It was great to stretch out, but no where as nice as flat beds. Great AVOD, food (for Y class, that is) and typical SQ service; I arrived feeling great.
The ICN-SIN sector, however, was much more full, may be 90-95% full in Y. Not so bad as it was a much shorter flight.
Flights home to the US were fuller as well, but I really enjoy flying SQ and their 77W seats are great. I'd rather pay a little more $ to fly SQ than UA any day to get to SIN. Hope this helps.
Have a great flight!