Just thought I would mention my very short article on some beginning
points on how to "survive R." When I first started with R I had no
idea how the attributes system in R worked (and I had read a few good
books on R). I have some notes how to inspect objects (using, unclass
(), attributes(), methods()) which are useful. Also some wiser people
added info in the comments (like str()).
http://www.win-vector.com/blog/2009/09/survive-r/