I've recreated an instance of River4 on Heroku, this time making a clone of the River4 repository rather than creating my own from a downloaded copy of the files. Now after Dave makes updates I should be able to do "git pull origin" and then a "git push heroku master" to update the app instance on Heroku.
One of the reasons why I have recreated my Heroku version of River4 is that some folks on the support email list have said that it costs more to run River4 on a server that is not on EC2 like Heroku. They believe that you aren't charged for network traffic within Amazon's data center.
The information that they provide is not consistent with my experience. In August I ran River4 exclusively from Heroku and my total bill was $10.94, with a little less than half of that for S3. I got charged $3.77 for 753,787 PUT, COPY, POST, or LIST requests, and $0.50 for 1,261,298 GET and all other requests. Clearly, S3 tracked my I/O traffic with Heroku and charged me for it, even if it was on their internal network.
I've been running River4 for almost 66 hours, and so far my my S3 bill is $0.69, 122,956 PUT, COPY, POST, or LIST requests and 169,752 GET requests. It seems to be in line for the charges I ran up on Heroku.
Right now I have my Heroku copy of river4 turned off but I could flip the switch to it in the future should I need to do so.