On my 11 inch I use a single pane. On the 15" it works well when the laptop is on my lap, but less so when it's on the desk but, then, it has two larger monitors, one horizontal and one vertical, so I can still use the two-pane arrangement (typical use is program and test files side by side).

I cut my teeth on the Apple II+, with 40 columns. I agree that 40 columns would be silly, but keeping the text column narrow so that eyes don't need to move too much helps a lot. It's a readability trick used in print since ever. From my position, the horizontal screen spans about 60 degrees, which feels excessive. By the time my eyes marched from left margin to right margin, I already forgot what I was looking for.

I did read the second paragraph, which makes the first paragraph all the more confusing. First you utterly dismiss the argument on an unreasonable basis, and then in the second paragraph you acknowledge that it's useful to be able to do that.

> Just to be sure, I just tested on my notebook screen (13"): 2x80 doesn't fit with a comfortable font size for me, so maybe we should start using 70 chars?

Sure, YMMV. Even when that turns out to be too small for you, less text per line in the editor leaves more horizontal space for something else, for example a file browser sidebar or a terminal. I've done 2x80 on netbooks for what its worth, but the font size that required probably wouldn't be comfortable to me today.