Jeroen Ooms did for R what Google did for editing documents online. He created several software packages that help running R with a nice frontend over the Internet.
I first learned about Jeroen’s website through his implementation of ggplot2 – this page is useful to generate graphs with the powerful ggplot2 package without R knowledge, however it is even more helpful to learn ggplot2 code with the View-code panel function which displays the underlying R code. If you are into random effect models another package connected to lme4 will guide you step by step through model building.
I think this is a great step forward for R and cloud computing!