I think the main problem is in which direction one is headed.
Eg., ATL-FCO (Rome-Fiumicino) is a night flight but it is only dark for maybe 6-7 hours of a 9 hr flight. Hard to sleep well on that one. However try flying back from Europe to Atlanta in the winter on a flight at leaves VERY early (around 0400-0800). Flight times average 10 hours and it will be dark for all but the last hour of flight. A heck of a lot easier to sleep on.
I flew on Delta from Dubai to Atlanta a month and a half ago. We left DXB at 2245 and arrived in ATL at some time right before sunrise (it was still dark whilst taxiing to the concourse, but sunlit whilst driving home to the city). About 15 hours inflight ALL during the night....I tell you though, that was some good sleep!
To Asia it's a different story. Most transpacific flights leave the east coast around 1200 and so it is daytime all the way until one reaches the International Date Line. If it's winter time one will then see dusk. If it's summer time...sorry it'll be bright the entire way over. I flew on Korean Air a few years back from ATL-ICN in February....it was dark for the last three hours in flight (over Siberia there was light but it was dark when we arrived in Seoul-Incheon), however I flew on United from Atlanta to Osaka (via ORD) in the summer time and it was daylight the entire way over...sheesh that was a bit difficult...but nothing a bit of champagne in Business Class couldn't fix!