Who said user feedback isn't easy to get?
One of the products I'm working on has a design choice to be made. It's about the types of lines that should be used to represent an inner join vs. an outer join.
Take My Poll
and let me know what you think.
Update: Some respondees asked about other options (other than thick or thin). While I'm trying to keep it to those two, but I've updated the poll to allow you to enter your own suggestions as well.