Please, add the ability to properly have two legends with the same concept, for example two legends related to the size.
If I run this simple code
DF <- data.frame(x=c(1,2,3,4), y=c(1,2,3,4),
z=c(3.4,1.2,1.1,0.5))
ggplot() + geom_segment(data=DF, aes(x=x, y=y,
xend=x+1, yend=y+1, size=z/10 ), colour="blue") +
geom_point(data=DF,aes(x=x, y=y, size=z)) +
scale_size_continuous(name="size")
I get the legend for two variables that define sizes but they overlap and they are unusable.

I have also tried using
+scale_size_continuous(name="size1") + scale_size_continuous(name="size2")
But it generates an error.
I've asked this at ggplot2 github but they told me to do it here.