I am running R version 3.1.3 (2015-03-09) with RStudio 0.98.1103 under OS X 10.10.2 (Yosemite). I migrated to this machine recently and moved files and applications (R and profile files included) with OS X Migration assistant. 
R has worked perfectly until I tried to install.packages(). The function initiates but it doesn't produce any printout or terminate. I tried different things:
- I removed my 
.Rprofilefile which indicates my package folder and restart R; - I tried different mirrors with 
install.packages('RMySQL', repos='http://cran.us.r-project.org'); - I tried 
install.packages()both from shell and from R GUI; - I tried to upgrade all packages with RStudio.
 
I never encountered an error message of sort and none of the above worked or produced any result.