Every route is different but I'm mostly flying between the US and NRT and I was about 50% this last year. Year before that, I was 4/6 so the odds have gotten worse for me. Europe looks much easier than Asia because the routes are shorter (if you're on the East Coast). If you do go for them, you should definitely waitlist ASAP. There were times when I cleared months out and then the flight became booked solid (i.e., no way it would have cleared if I waited). The plus with clearing early (especially on a 747) is the ability to choose the best seat instead of at the gate, when you'll get the worst.