Comment by zackzackzack

Some notable features:

Call outs to R code http://www.wolfram.com/mathematica/new-in-9/built-in-integra...

Social network analysis http://www.wolfram.com/mathematica/new-in-9/social-network-a...

Computation bar http://www.wolfram.com/mathematica/new-in-9/next-computation...

Sigh. I dream of Mathematica being open source.