Hi all,
I seem to remember a few recent requests for a "lines only" mode in pen tool (can't find the related emails or bug reports offhand). [1] For my LPE work I had implemented this a short while ago anyway (if for different reasons), but so far it has only been used internally. Now I added a new button to the pen toolbar to make it publicly available. You may want to give it a try and see if it is useful. All it does is prevent you from making curves: each mouse click automatically addes a new line segment, regardless if you are dragging or not.
Personally, I'm not too convinced that it's of great value but other people may have different opinions. If it turns out to be useless, feel free to ditch it again. :) If you want to keep it, you are welcome to design a more beautiful icon and/or find better descriptions, too.;-)
Max
[1] This one seems to be along these lines, too, but it's very unspecific: