R is indeed quite weird when you get to internals. What's the problem you have with S3 though? It has it's limitations, but since I've first seen it, I thought

R is indeed quite weird when you get to internals. What's the problem you have with S3 though? It has it's limitations, but since I've first seen it, I thought it was by far the single most convenient and intuitive OO system out there... But yes, can't use it for everything. S4 is a bit ugly but still kinda workable -- the real problems for me start when you need to deal with environments and expressions and such, but is it really so often necessary to go there when you are designing your own tools (which I guess is what you're doing?) As for the real-world percentage, it varies depending on the job -- R is primarily designed for the people who spend most of their time looking and thinking about the data, rather than the code.