Can HTML5 and CSS3 work for us today?

Any tool or technique should only be used if the application requires it. As frontend developer/designers, our projects typically come with a finite amount of time and resources available to make them financially viable.

As Internet Explorer 7 and 8 don't support the new semantic HTML5 elements or CSS3 properties as standard, if the vast majority of visitors to a site use Internet Explorer 7 or 8, it doesn't make a lot of sense to concentrate your resource on producing a responsive HTML5 and CSS3 based design for it. That doesn't mean doing so is an impossible task. Solving Cross-browser Responsive Challenges, there are a growing number of tools (referred to as polyfills as they cover the cracks in older browsers) to patch browsers (mainly Old IE) lacking support for more recent browser features, but adopting a sensible approach to the implementation of a responsive web design from the outset is always the best policy.

In my own experience I typically ask the following from the outset:

• Does the client want to support the largest growing market of Internet users? If yes, responsive methodology is suitable.

• Does the client want the cleanest, fastest, and most maintainable code base? If yes, responsive methodology is suitable.

• Does the client understand that experience can and should be subtly different across different browsers? If yes, responsive methodology is suitable.

• Does the client require the design to look identical across all browsers, including IE 8 and lower versions? If yes, responsive design is not best suited.

• Are 70 percent or more of the current or expected visitors to the site likely to use Internet Explorer 8 or lower versions? If yes, responsive design is not best suited.

To attempt to put the philosophy of responsive web design in a nutshell, I would say it's the presentation of content in the most accessible manner for any viewport that accesses it. Conversely, a truly "mobile website" is needed when an experience requires specific content and functionality based upon the device accessing it. In these cases, a mobile website presents an entirely different user experience to its desktop equivalent.