400k now. Yeah pretty crazy, I've almost used 40 gb of disk space, and if the traffic keeps up, it'll be a TB of submissions. That being said, it's also a bit unreliable and users often have connections fail when submitting, but it's really pretty solid. I've now switched to Dreamhost PS, so it's a little more expensive, just to make sure it's a bit more reliable.
How many page views do you guys get? Out of the 34 servers, how many are front end? I want to get an idea of the # of page views per front end server your rails app is handling.
BTW, your dreamhost account was able to handle 100K submissions? not bad!