Twitter open sourcing bootstrap just made the whole web better. Open source projects especially. Projects like https://github.com/dcramer/sentry benefitted a lot from bootstrap.
While I agree that Bootstrap is awesome (I use it myself), it's worth pointing out that what Twitter open sourced was not the magic of their core product, but rather the templates that they use to create internal applications. If you look at twitter.com, you don't see any of the same elements that are included in Bootstrap.
