I've also seen a speedup in Rails app boot time (the require optimizations):

1.9.3-p194: 11.8s

1.9.3-p385: 9.9s

2.0.0-rc2: 6.1s!

Tests were done with `time bundle exec rake environment` 5 times, dropping the highest and lowest and getting the mean of the rest (lazy snow day benchmarking). Very exciting!