For what its worth, I fly to NRT about 10 times a year, and I have _never_ cleared a SWU at booking time in the last 2 years. When I book (about 4-6 weeks out on average). That said, I do clear approx 75% of the time on waitlist. Its been worse lately (not clearing outbound, but clearing inbound).

My home base is SFO, but I've flown from LAX, DFW and ORD, price depending.