Who is the books audience? Its a second book. A second book to a theory book. A second book to a textbook. A second book to a your lecture notes. It will never be ~the~ book for a topic by itself, but it just a brilliant job of filling gaps.

I picture it like this: if your going into a graduate program that uses R buy this book and you will use it. 2 out of 3 courses I took in spring semester used R heavily. I am surprised none of the instructors had the line "Recommended for students continuing in R is MASS..." in their syllabus. Because that is exactly what I would say. This is one of those books you want to get early, and keep it around.

It never explains enough of the statistics to stand on its own; however, its coverage of R and R packages is more complete than anything I have found elsewhere. And having got it a year after I first started using R, I am sad I didn't get it sooner =)~

If you're changing topics alot like a student does is it ~the~ desk reference for R? Probably. Maybe I will run into a better one in a few months though? I dunno.. you get it and tell me.