I was playing around with Twitter Bootstrap yesterday and managed to very easily migrate my App Control website over to use it as a way to clean up the UI and get it looking a little more consistent.
It provides some nice looking default looks and easy to use css classes to apply. It’s hard to imaging doing another site without using something like twitter bootstrap as a starting point.
Something I’ve found recently is just how difficult creating a great UI can be. The finishing touches on making things line up just right or animate fade ins and dropdowns is surprisingly difficult when taking into account all the various browsers out there.
Twitter bootstrap gives you something professional looking by default and is a fantastic starting point for future customization. If you have a web project I would encourage you to look at it.