Do I need to learn R?

I've been focusing mostly on learning python and it has allowed me to work through some intros on machine learning and data mining, and build a few applications for practice. I'm trying to think of what I should focus on next to get past the "beginner" stage, and I'm wondering if anyone have any recommendations for what someone in my situation should be learning next...should I learn something more specialized toward statistical analysis like R (I've got a decent base in pen and paper mathematics & statistics) or should I just keep using python to tackle more & more challenging problems?

My main interest is the implementation of machine learning in internet applications - finding where and how to apply them on the web in the most useful way. My goal is to be able to find new and creative ways to apply ML/AI toward making web applications better and more useful. I'm perfectly willing to spend years to get there, just wondering if someone with experience with this can help work out a roadmap.