I have been using R for years, but recently I have been working on a few Data Science problems that are natural in R. As a result, I have been getting a lot better and utilizing mostly online resources to improve my R skills. This has been fun and I am getting a glimpse of what the language can do and what it just does not do (data sets bigger than a few Gigs). Here are a few links that I have been enjoying.
This is a great practical journey into getting things done in an applied field. the fact that it is psychology makes almost no difference. http://jeromyanglim.blogspot.com/2009/06/learning-r-for-researchers-in.html
The awesome Joe at Revolution Analytics has put together a great description of the process of learning R and some great tips. http://www.inside-r.org/howto/how-learn-r
I would add more but these are such a great start and they have linked to all my other favorites.
A Fine Point 