Lucky for me - I go to Canada 3-4 times a year for business
Sadly for me - It means I fly Air Canada.
Three times in dealing with Air Canada's particularly low standards of customer service I have pulled out my cell phone and taken a photo of the agent "for my records". I have had one lady go into full meltdown and get the police involved. The responding officer asked me to delete and I refused, he told the employee that he couldn't make me delete it and it was a civil matter.
Now, to AC's credit, I haven't heard of them deboarding a 69 year old Doctor with force, but using a camera or cell phone to document things has its advantages. I think the United passengers were correct in doing so.