The biggest focus on this release seems to be performance as Apple focuses on results of various benchmarks, likely also so that Apple can continue to call Safari the "world's fastest Web browser." They even have shiny graphs to back up that claim. Judging by the charts, Safari is a whole lot faster than Firefox, and slightly faster than Google Chrome. I put this mostly up to WebKit, which is the same rendering engine used in Chrome and Safari, versus Gecko, which is used in Firefox.
So, relying on simple human experience which, at the end of the day, is all that really counts, Safari 5 seems no faster to me than Safari 4. The sites I visit in Safari 5 feel no faster at all. Then again, when everyone was saying that Google Chrome was so much faster than Safari, I didn't experience that either. I can definitely tell that Safari (and Chrome) is faster than Firefox, however.
Support for extensions
So aside from these speed boosts, is there anything else that makes Safari 5 compelling? Absolutely! Finally, Safari has support for extensions. While they're not technically available yet via Apple, you can enable extension support already. In the Advanced preferences pane in Safari, enable Show Develop Menu In Menu Bar. Then, on the menu bar, select Develop and then Enable Extensions. And while Apple is just now accepting extensions for their Extensions Gallery, you can get some already via the unofficial Safari Extensions site.
When Extensions are enabled, a new pane in the Safari Preferences window shows up -- aptly called Extensions, and it is here that you can see the installed extensions. Downloadable extensions will have the file extension .safariextz and can be downloaded in Safari. Unlike Firefox, the extension will be downloaded to your Downloads folder (unless you have told Safari to open "safe" files after downloading). Double-click the Extension file for Safari to install it. Once that is done, go to the Extensions Preference pane and if the extension is configurable, you will be able to configure it there, as well as choose whether or not to have it enabled.
One great extension that has been ported from Google Chrome is AdBlock, which gives the ability to block those annoying ads on Web sites. Another very cool extension is SafariRestore, which will restore your previous browsing session upon restarting Safari.
Apple can talk all they want about speed improvements, but the real feature with much awesome-factor is the ability to finally have extensions. This has been such a critical feature missing in Safari for years, that it is great to finally have it.
Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.