If you're going to download the Mac binaries for the latest R, you will see that they come in "Snow Leopard and higher" and "Mavericks and higher" flavors. If you run Mavericks, the latter is a natural choice, though the former clearly says "and higher" too, so it's got to be a valid option as well.
As it turns out, it's the better option, at least as of this writing.
The Mavericks build crashes with a segmentation fault upon attempting to load either the caret or data.table library, as reported here and here. A brief search through the R-SIG-Mac Archives returned no useful leads for fixing the problem.
Dropping the Mavericks build and installing the Snow Leopard one gave me back both caret and data.table. This works for me.
> sessionInfo()
R version 3.1.0 (2014-04-10)
Platform: x86_64-apple-darwin10.8.0 (64-bit)
locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] RCurl_1.95-4.1 bitops_1.0-6 scales_0.2.4 ggplot2_1.0.0 reshape_0.8.5 data.table_1.9.2
[7] MASS_7.3-31
loaded via a namespace (and not attached):
[1] colorspace_1.2-4 digest_0.6.4 grid_3.1.0 gtable_0.1.2 htmltools_0.2.4 munsell_0.4.2
[7] plyr_1.8.1 proto_0.3-10 Rcpp_0.11.2 reshape2_1.4 rmarkdown_0.2.46 stringr_0.6.2
[13] tools_3.1.0