In a blog post, Nick Mackechnie, a senior Microsoft account manager in New Zealand gave the warning:

However, browsing with this default setting may cause content written for previous versions of Internet Explorer to display differently than intended. This creates a call to action for site owners to ensure their content will continue to display seamlessly in Internet Explorer 8. As such, we have provided a meta-tag usable on a per-page or per-site level to maintain backwards compatibility with Internet Explorer 7. Adding this tag instructs Internet Explorer 8 to render content like it did in Internet Explorer 7, without requiring any additional changes.

We are encouraging site administrators to get their sites ready now for broad adoption of Internet Explorer 8, as there will be a beta release in the third quarter of this year targeted for all consumers.

It's not like this is new news; it was stated when IE8 Beta 1 was released, and many broken sites should have already warned enough webmasters. Still, Microsoft is nothing if not cautious.

Site tips are here, and involves setting the X-UA-Compatible property to "IE=EmulateIE7." Of course, past builds of IE8 have included a prominent button, "Emulate IE7," that enables end users to switch modes. It's unclear if this button will still exist in Beta 2 (my guess is it will).

Source: By Tech Ex http://technologyexpert.blogspot.com/