[bhaak]

80 columns would be enough most of the time.

But how often do you really have 80 columns? With indentation you chip away on the left side and with a few indentation levels you have not as much space left.

[rbanffy]

Three or four levels is most likely too deep.

[bhaak]

Depending on language that's easily reachable with sane code.

One level of indentation for the module/class level and another one for a method. Already at two levels.

Within a method, two levels of indentation are by far not extreme.

[rbanffy]

Good point. I was thinking from the base of the code block :-(

/me slaps forehead.