And this is why I gave up on R for other things than ad hoc data exploration (don't get me wrong; it's killer for that). When I finally learned there were no less than four system of OO buried in base R, and still people were unhappy and inventing more, I realised that as far as well structured programming goes, R is kind of beyond help at this point.
From what I can tell, my biggest disappointment with ggplot2 is not addressed - the fact that ggplot evaluates all references not found in the data frame to be plotted in the global namespace. The result is that you can't actually make reusable, composable plots in a reasonable sane way. It sends the whole illusion of composability that ggplot()'s '+' syntax suggests might be there right down the tubes. My plots were all more reusuable before I ported them to ggplot (ie, in base graphics).
Apologies for the whining, and congrats to Hadley!