I never had to stand in line but did have to wait. My maximum time was about 2 hours and it was well worth it. They had the buzzer system so we just explored the area till they had a table for us.
Depends on the restaurant. If I was traveling abroad and wanted to try a famous restaurant I would wait. I think the longest I waited was 45 minutes and it was standing. I don't sit a lot at work so I don't get the big deal about standing.
As so many others already said, it depends on the restaurant, but also what time it is, how hungry I am, how much money I have, how expensive it is and so on. There's no clear cut answer, but let's say half an hour as a good general rule.
Yeah have before in Japan where that kind of thing is common because the restaurant is small and the food good.
And a few months ago in Sydney I waited in line for 30 minutes for a camel burger at the Ramadan Night Markets. It was sooooo good that I went lined up later for a second.