1.9.3 is great for production. You give up a bit of memory savings compared to REE (since Ruby proper won't be COW-friendly until 2.0), but 1.9.3 in general is

1.9.3 is great for production. You give up a bit of memory savings compared to REE (since Ruby proper won't be COW-friendly until 2.0), but 1.9.3 in general is faster, has a lot more features, and is widely supported by gems and libraries now. 1.8.7 has been EOL'd, which is as good a reason as any to upgrade.