In production use, we found we could run double the load on our servers with 1.9 than we could with 1.8. Switching to 1.9 kept us running our app on a cluster

In production use, we found we could run double the load on our servers with 1.9 than we could with 1.8. Switching to 1.9 kept us running our app on a cluster of 8 servers as our user base grew, saving us the monthly rental of 8 servers and the overhead of running twice as many web servers. We never measured how much longer our tests took to run though, since our customers were only ever running in Production mode