When designing a logo it’s important to consider how it will look at different sizes. On the web, it will be seen on screens of all sizes from tiny smart phones to large desktop monitors, and it may be used as a tiny avatar, a small ad, or a larger featured image. In print, it may be used on small business cards, a tiny bug in a credit line, larger brochures and advertisements, maybe T-shirts, and possibly even huge signs or billboards.
Joe Harrison has created a showcase of logos that do more than just resize in response to smaller or larger use-cases. On his site you can see how several big-name logos transform as you resize your browser window—not merely resizing, but actually changing form to suit a larger or smaller space.
Here is just one example. Check out the Responsive Logos project for more.