To help me keep my design relevant I decided to some research into existing responsive design. One site that I really liked was the Mozilla website, below is the full sized desktop view:
The first break-point (tablet view) only restructures the second banner, bringing the list items below the 'Different by Design' text. The logo and top navigation are also scaled to give the site cleaner vertical alignment.
The next break point (mobile/small tablet view) brings the first drastic change to the structure of the site. The top navigation is condensed into a drop-down box to help optimise space. The logo and banner are also totally restructured, losing the bullet points.
The content boxes are stacked vertically, rather than arranged side by side.
The site also accommodates much smaller mobile phones with its last break point. Apart from scaling, the only thing that changes is the 'Different by design text is stacked.
From looking at this website and others (Starbucks, Mashable) the most drastic changes happen when changing from tablet down to mobile view (structure and navigational changes), with the difference in tablet and desktop view mostly being about visual reordering.