Although i have a simple CSS framework using it with any new project as freelance or in Bayt.com projects, but after i found twitter bootstrap i am impressed for how can it help me, and its a weapon of choice for me for this reasons:
- Easy to work with.
- Streamline workflow and they make web design a joy.
- Improving productivity and refining the quality of your layouts.
- Working with Cross browsers.
- Practically a necessity as far as responsive design aimed at a wide array of formats and screens is concerned.
- Built on HTML5 and CSS3 Integrated.
Here is most Incredible Sites Built With Twitter Bootstrap: