Adjust position and font size of legend title in ggplot2

Yes, using a feature of the new 0.9.0 version, guides:

p + guides(colour = guide_legend(title.hjust = 0.5))

You can read about guides here.

If you are using ggplot 0.9.1 version, this works for changing the position and size of the legend title

p + theme(legend.position=c(0.85, 0.3),legend.title=element_text(size=14))