David Yanofsky did a link-rot analysis of The Million Dollar Homepage and found that 22 percent of its pixels are dead:

These non-functioning links account for 221,900 of the million pixels—$221,900 worth of real estate, assuming the pixels have kept their value in the last eight years. The atrophy of links has been shown to stabilize over time, meaning we should expect fewer than 22% of links to break over the next eight years. The longer a link continues to work on a webpage, the longer it can been expected to work into the future.

Nonetheless, it remains a problem for thought experiments and seminal works alike. Researchers at Harvard found that at least 50% of URL-based legal citations in US Supreme Court opinions, for instance, no longer point to the originally referenced material.