I agree with Caleb. When your developing a consumer-web product then it matters a great deal, people have high expectation in terms of UI/UX and won't wast their time figuring out how your app works. Make it simple, make it easy, make it beautiful. For B2B software, it matters less, but that's changing quick. If you can develop a B2B product that has UI/UX of a consumer product you will have a big edge over competition. I am seeing more and more startups in the B2B space that are using cutting edge UI/UX tools, like D3.js, and architecting software with responsive design in mind.
Some tools that you might want to look at;
Bootstrap (or other UI frameworks)
Angularjs (if your looking to build SPA (single-page apps), rich-apps)
Phonegap (more of a framework for mobile development)