I've taken quite a few photos on board aircraft and in lounges and I've never had any issues on board. I was onced asked to stop in the Perth Qantas Club, because "taking photos of the runway is a security risk", err, whatever.

As has been said in these threads before, the key is discretion. Never take photos facing from the front into the cabin (capturing people facing the camera), never take photos directly of the crew without their permission, don't use flash.

On my recent flight from SIN to SYD in F there was someone who kept using the flash during dinner which was a real pain. The crew (who were amazing!) recognised that this was annoying the other passengers so had a quiet word.

The excuse of wanting to take photos is always the one that I use to visit the cockpit after landing and it normally always works. Most crew are interested in my camera and whether it's a hobby or a profession. Sometimes you find crew that are photographers themselves too.

Some airlines do embrace cameras on board more than others. Emirates for example seem to actively encourage people to take photos at the bar on the A380. Perhaps they see it as free advertising as the photos will invariably become socialised on Facebook/Twitter etc.