I think it depends on how often and for what purpose you intend to use ggplot2.
I mainly use ggplot2 for graphics in publications. This means that I tend to need the more advanced features and so I have never bothered to learn about qplot. Also, since I have around four publications a year, I'm not using ggplot2 enough to be really comfortable with the syntax and so concentrating on a single aspect seems optimal.
However, if you get new data sets each week, then you are probably interested in quickly exploring the data sets and producing good quality plot. In this case, learn both. You will get enough practice with the syntax and will (eventually) save time with qplot.
