Count me in as a vote for it was rude.

It's one thing to leave it there for hours. Another for just a few minutes to use the restroom or whatever. 1/2 hour is my line in the sand.

I'd never do it cuz I'm afraid of theft, but if someone did, I'd respect it for 1/2 hour of time. Beyond that, it's "unattended luggage" and I'm calling security or other airline personnel.