Here is a simple look at the duration it takes for previous Flash Player versions to spread¹…

• Flash Player 5 - over 5 years to reach 96% or higher adoption
• Flash Player 6 - over 3 years to reach 93% or higher adoption
• Flash Player 7 - just over 2 years to reach 85% or higher adoption
• Flash Player 8 - just over 2 years to reach 86% or higher adoption
• Flash Player 9 - in roughly 6 months since release (released in June 2006, currently January 2007), has worldwide penetration of 35%

Comparison
This comparison will match Flash Player to PHP. Although this may seem like an apples to oranges comparison (client-side technology vs. server-side technology), I chose this because PHP is one of most popular web technologies currently used today. I should make it clear that the measure for PHP is based on all computers deploying and/or hosting websites, while the comparison with Flash Player is measured against all computers connected to the Internet.

PHP 5, the latest release since PHP 4, has found usage on roughly 1.82% (4.89% of 37.19%) of websites after 2 years of reaching a stable version².

Flash Player 9, the latest release since Flash Player 8, has worldwide penetration of 35% after only roughly 6 months of release.

¹http://www.adobe.com/products/player_census/flashplayer/version_penetration.html and http://www.communitymx.com/content/article.cfm?cid=511F7
²http://www.phparch.com/issuedata/articles/article_226.pdf