I'm actually not too bad at design, and really enjoy it – my other startup http://www.pacpacs.com was designed by me which I don't think is too bad :-)

... where bootstrap really shines is that I had a working basic version of the app running and looking pretty good about 6 hours after the idea, I would have spent longer than that in photoshop staring at color swatches. It's the perfect prototyper.