Safari 5.0 included the capability to run extensions but it was turned off by default and the extensions that were available were not easy to find. Now Apple has turned extensions on by default and provided a web site for extensions available for installation.
The installation of extensions in Safari is probably one of the best aspects of the feature. To install an extension, I simply clicked an install button on the web page and that was it, the installation happened instantaneously with no progress bars or need to restart the browser.
I found many welcome extensions at the Safari Extensions Gallery that can improve everything from web page displays to twitter and Facebook use. Still, compared to the number of extensions available for Mozilla Firefox, Safari has a very long way to go before they catch up.
To try out the new Safari update go to www.apple.com/safari/