I have migrated the website layout to ZURB Foundation, mainly out of curiosity for the framework.
The migration has been painless and relatively fast (thanks also to Jekyll, which neatly separates presentation from content).
The new layout is, in my opinion, cleaner. I did not have to customize much, but I did not have any difficulties in deviating from the standard here and there, either. This is something which I cannot say of Bootstrap.
Both frameworks are great; the first impression is that ZURB is probably more effective for websites, while Bootstrap provides a bit more support for WebApps (e.g. type ahead is available out of the box for Bootstrap; a Bootstrap themed date picker is also available — two components I use quite often). I did not have time to test ZURB on a WebApp yet, e.g., so see how well it integrates with the corresponding jQueryUI elements.
There is an excellent comparison of frameworks available at Vermillion’s Comparisong of Responsive Frameworks.