I don't get noticed - or no one actually cares.

My tips:

General:
There's a disable flash function in 99.9% of cameras. Use it
Avoid people unless they want to be in the shot (does happen)
I avoid taking pics of cabin crew unless they're really in a good mood and want to play the game

Food:
If its dark, You might have a light above you - use it!
There's normally a night mode - this helps too.
For people with SLR type cameras (the big chunky things), there is a reason why you have ISO800/1600/etc. This is one of them for night shots!
Uses both sides of the armrest and hold your camera with two hands. This will help you steady your shorts .

Out of the window
- Snap happily away. Ignore the persons pain next to you. Advise them you're a geek who likes the view 41000 feet down. If they really get annoyed... show them your pictures (don't show them any "alternative" images you might have taken though. unless you REALLY want a quiet flight) .
- This works from the isle seat too
- If you're trying night shots, a dark cabin is a must. Otherwise you'll get reflections everywhere.
- For people with SLR type cameras (the big chunky things), there is a reason why you have ISO800/1600/3200. This is one of them for night shots!
- Blur is not a bad thing if used creatively. Example: Night takeoff, hold the camera sorta still, take picture - you'd be surprised at the results.

You might want to look at the Travel Photography forum for all sorts of fun pictures that have been taken.