For the line tool, dashed lines and arrows would be very neat (like in Paint.Net)

This is one of the features that I really need. Starting, ending arrow support and different line styles like dashes, dots etc. Paint.net has a nice solution.

I can not see any arrows for lines in Pinta. Actually it is what you need most to give directions through screenshots. Great in Pain.net. To my surprise such basic feature is missing in Pinta.

I offer to pay for this feature!!

Yes, please!

Yes, I installed Pinta on my Mac because I use Paint.net on windows all the time. I was a bit disappointed to find that Pinta lacks line styles and arrows. Try making a stamp with half holes around the edge without the dotted line to see how important the line styles are.

Planed for Google Summer of Code 2013 project by Andrew:
https://groups.google.com/forum/?hl=en&fromgroups=#!topic/pinta/sjEXOTwSs-A

It is planed to be implemented in mid September.

any updates?

@Marc, March 1, 2015 it was released 1.6 that has support for arrows and dashed lines. See download page: http://pinta-project.com/releases

Arrows and dashed lines work perfectly.