My company's direct competitor contacts me on a weekly basis to try and poach me. I'm super, super highly qualified for that job, and I could probably leverage a massive raise... but I would feel so, so dirty for doing that.
It's fine to go to a direct competitor, I think. I'm just saying working for both at the same time would be... well, probably career-ruining in my line of work. I believe our little industry has an unwritten rule of 2-week minimum cooldown when switching companies.
It's nice to know I still have morals. ;)