If you're a website developer then the newly released Internet Explorer 8 means there is yet another browser you need to know how to develop for. IE8 is easier to develop for than any other IE browser so far because Microsoft is finally making a real effort to be standards compliant.
Microsoft has also released a readiness toolkit. And the developer's section of the kit documents everything a developer needs to know about IE8.
IE8 Readiness Toolkit - Developers