I did a survey of what naming conventions that are actually used on CRAN that got accepted to the R Journal :) Here is a graph summarizing the results:
Turns out (no surprises perhaps) that lowerCamelCase was most often used for function names and period.separated names most often used for parameters. To use UpperCamelCase, as advocated by Google's R style guide is really rare however, and it is a bit strange that they advocate using that naming convention.
The full paper is here:
http://journal.r-project.org/archive/2012-2/RJournal_2012-2_Baaaath.pdf
