From the 'what will Apple announce at WWDC' files:

It's official - Apple's Safari 4 is now out of beta. Frankly, I'm not surprised.

I've been running Safari 4 (on a Windows test box) since February when the first Beta came out. Since that time, I know that Apple has updated Safari at least once (mostly for security).

In my experience, Safari 4 as a beta was already production quality so it's not surprising that the it's now final. The key things about this release are the same themes that highlight new Google Chrome and Firefox 3.5 releases -- namely faster JavaScript (in Apple's case they call their engine Nitro now) and HTML 5 support.

For Safari 3.x users, Safari 4 is a huge leap forward, the speed of the browser is something that actually changes the browsing experience. The top sites feature, which is Apple's approach to show users the top sites that they've visited is a neat 'eye-candy' feature.

HTML 5 support in my view is the item that will really help to literally change the web experience. Among the HTML 5 supported features in Safari 4, Apple is supporting offline storage, which means that users can access some of their cloud/on-demand data - locally. Offline storage is the standardized approach to what Google is trying to do with Gears. It's not yet widespread across the internet as a whole, but it will be (at least, I think so).

In terms of competition, Apple states in its release that, "Safari quickly loads HTML web pages more than three times faster than IE 8 and three times faster than Firefox 3."  Mozilla's MIke Beltzner has told me that Firefox 3.5 (which is nearing completion) is three times faster than Firefox 3 as well (which means that Safari 4 and Firefox 3.5 are nearly the same speed?).

Apple also states in its release that, "Safari is enjoyed by 70 million users worldwide," with Safari 4 now out for both Mac and Windows users, I'd say it's a safe bet that Safari 4 is likely to help Apple grow its base.

**UPDATE**
Just finished going through Apple's security notes on the Safari 4.0 release.

There are a lot of updates, some more serious than others, but nothing too shocking in my view. WebKit gets a bunch of fixes for images handling and even cross site scripting issues. Safari's private mode also gets a fix to actually keep cookies private -- so if you were using the beta before - guess what? - your sessions were not as private as you may have thought.