Twitter seems to really rag on rails but at the end the graph looked pretty good to me for their old architecture at the 95th percentile given their traffic.
Most sites won't even get 200 reqs per second total, and it's great to know that rails can pump that out on a single machine for a non-trivial app.
200 * 60 = 12,000 reqs per minute
12,000 * 60 = 720,000 reqs per hour
720,000 * 24 = 17,280,000 per day
