Assuming they were already running Ruby 1.9.x, they probably saw a smallish increase in response times moving from 2.3 to 3.0. I've seen that on two separate, large projects.
There is a drastic decrease in response times with switching from 1.8.7 MRI or 1.8.7 REE to 1.9.x MRI.
There is a drastic decrease in response times with switching from 1.8.7 MRI or 1.8.7 REE to 1.9.x MRI.