How do I access data on my EBS Volume from R-Studio Server on Ubuntu EC2 Instance
I see this question got up-voted so someone else is looking for the answer. Here it is: 

I was logged in as the default user on Ubuntu instance when i did the 

$s3cmd get s3://data-analysis/input-data/filename.csv


The data got saved from the s3 bucket to the home directory of the user named ubuntu. this can be verified with : 

$ df -h /home/ubuntu/ 

Since I had followed randy zwitch's tutorial on installing R on aws - i had created a user named rstudio and that was the user name I was using to log-in to rstudio server. Hence I had to move the file from the default 'ubuntu' user's home directory to the user 'rstudio'. this can be done with: 

$ sudo mv /home/ubuntu/filename.csv /home/rstudio

Happy to answer follow up questions.