More outstanding issues are biting me with Internet Explorer 7, specifically these two well-known issues:
IE doesn't render table row elements <tr> unless they are added to an explicit <tbody> element. (The HTML and XHTML DTDs allow <tbody> to be optional/implicit.)
IE doesn't accept XHTML attribute names as XML DOM setAttribute() keys, requiring instead HTML DOM HTMLElement member variable names. (The HTML DOM is defined as subclassing the XML DOM without overriding these methods.)
I'm now using the Internet Explorer Developer Toolbar, which comprises a few of the features of Firefox's Web Developer Toolbar and Firebug extensions. It's really helpful in diagnosing these IE issues.
Looking through some of the unofficial bug lists for Internet Explorer, you start to get an idea of just how far behind Internet Explorer still is.