The release candidate isn't dramatically different from the public beta, but there are a number of tweaks and refinements that make IE9 feel more usable and put-together.

When I r, I noted that I wasn't a fan of how IE9 placed the tabs on the same line as the address bar. It made everything feel squished, and there wasn't enough space for more than a handful of tabs before tab names would become truncated to the point of being nearly useless. The IE9 release candidate fixes this issue to some extent: While it still defaults to having everything on one line, you can now separate tabs onto a second line by right-clicking an empty area in the toolbar and selecting "Show tabs on a separate row." Ideally, this would be the default behavior, but it's better than nothing.

In addition, the IE9 release candidate does a better job at keeping you informed on the status of a loading page. The initial IE9 public beta would show a spinning status indicator to show that the page is loading, but it would for only a second or two. If you were on a slower connection, the indicator would disappear before the site would load in, making it unclear if there was a problem with the site, or if it was still loading in. The release candidate shows the spinner until the page is completely loaded.

Microsoft made another tweak with the interface, by further shrinking the amount of window chrome and toolbars. The main toolbar is 5 pixels narrower than it was in the public beta. There is such thing as too little interface, though: This change is good for PCs with small screens, such as the netbook I'm using to test IE9 on right now, but it could be an issue for those with larger screens, since the "targets" for different parts of the interface are quite small.

Microsoft made various performance improvements in the release candidate; that said, we didn't have a chance to test its performance.