One of the most important features of Safari 5 is support for extensions: it's what Safari users had been wanting for a very long time, and it's a big deal. It's a big deal for users who want to customize their browser the way they want, it's a huge deal for developers who may start to charge for full-featured extensions in the future. Just think about Twitter clients or RSS apps living inside the browser.
Safari 5 has been available for 12 hours now, and some developers have already released their first extensions. Obviously these extensions are far from being "complete" and "full-featured", but still it's worth taking a look at them, as they're giving us a glimpse at what devs might offer in a few weeks.
It seems like Apple made extremely easy to turn stylesheets into extensions. If you were a Greasekit / Userstyle fan before, you know what this means. Thousands of website modifications already available to be converted for Safari 5. That's why we can already download a first version of Helvetireader and Elastic Thread's Instapaper Tools for Safari.
The extensions mentioned above are stylesheets, which become invisible to the user once activated. To turn off updates and uninstall them, you have to enter the extensions preference panel. What about additional buttons for Safari's toolbar? We're going to see a lot of them.
John Siracusa has created a custom reload button, very useful indeed. Victor Andrèe has developed a simple Gmail checker, and I have the feeling this kind of addons are going to be huge in the Gallery, launching this summer. Not to mention AdBlock for Safari, even though as a blogger I shouldn't suggest you to install it.
Last, Scribefire, a quite complex extension for Firefox / Chrome that allows you write blog posts from your browser. It's been ported by the developers from Chrome to Safari in under 90 minutes. It's already available here.
Apple made very easy for developers to convert stylesheets and Chrome addons into Safari extensions. If Scribefire took 90 minutes to be converted, imagine what's going to happen this week with all those Chrome extensions already out. Extensions are a big deal, and developers just need to figure out a way to start charging a few bucks for them. In an even better scenario, we won't see any paid extension and the Safari Extension Gallery will feature thousands of free addons for your browser.
The extensions I'm really waiting for? Tabs modifications. Twitter extensions. Simplenote. Google Reader sharing / notes tools. Extensions will deeply change the way we look at Safari.