Problem is, it wouldn't cure jet lag. When you land, your body clock is still out of sync. Example: an evening TATL leaving from DFW. You get anaesthetized at 7:30 PM shortly after hitting cruising altitude and you're awakened when you land in London 7 hours later. It's 8:30 AM in London. Problem is, it's 2:30 AM back home. It's going to take your body time to adjust to that even though you had 7 hours of sleep.

A few more pitfalls: you're not moving as much so there's the Deep Vein Thrombosis hazard. Artificially-induced sleep messes up your usual dream cycle so it's an abnormal type of sleep. And if the flight is diverted and you have to get off, you may be too oblivious to move (or you may leave a carry-on in the overhead bin).

I do use Ambien once in awhile, but not often for the above reasons.