There is no description of what the values passed to scale_*_manual actually represent. For colour-related scales, this is obvious, and some good examples are given, but for scale_size_manual, scale_linetype_manual, and scale_shape_manual, there is not description, and the user is relying on guess work.
Are the size values in points?
Would a link to the aes_linetype_size_shape (http://docs.ggplot2.org/current/aes_linetype_size_shape.html) documentation be sufficient? Or is more detail needed than what is presented there?
@BrianDiggs: that would probably be sufficient, yeah. Needs to be fairly prominent though.