I don't know enough about R. Here are two possibilities that I envision regarding the use of R:

1. You are fluent in R. You are able to readily use R for almost any kind of analysis. If you do not have experience with a package, you can learn it very quickly (minutes) and use it, assuming you are familiar with the analysis in general.
2. You are not fluent in R. You learned and use a few specific R packages based on your needs. You would not be able to easily use R for analyses that do not involve the packages you already know.

I know this is a false dichotomy, but it hope it serves to illustrate my questions. My questions are:

1. Are most R users fluent, or not fluent as described above?
2. I appreciate that becoming fluent in R would be most beneficial, but I also recognize that this would involve a significant time investment. For what types of users is such an investment worth it?
3. How many fluent users of R also resort to using other software?

I know these questions are relatively subjective, but I suppose so are other questions about R (e.g., "What R packages do you find most useful in your daily work?").

Edit: I will mention why I am asking. I have never used R and I perform relatively complex analyses regularly (e.g., propensity score matching, structural equation modelling, latent growth analyses, item response theory). I use three or four different statistical packages to perform these analyses. I have been lucky to find these software packages to do what I need, but I feel like eventually I won't be that fortunate. I am constantly debating learning R, despite being so very busy otherwise.