It's interesting how many people here say that they refuse to travel in coach, especially for long distances. Many say that they use their miles for upgrades or free trips in business or first.
I always use my miles for free trips in coach. To me, it's better to get two free trips in coach than one in business or first.
I've been on intercontinental flights in coach many times, and I've never had a problem. I've never flown anywhere in business or first class, so maybe I don't know what I'm missing, but it can't be so great as to be worth more than taking another trip another time.
Of course, I don't earn miles very quickly, so when I get enough for ONE free trip in coach it's a big deal!
Ed