I am really passionate about standards. It's important and something we aim for at 24SevenOffice. But building a AJAX based web-application with the look and feel of a traditional Windows based application is not an easy task by itself. To cope with the differences in the various browsers creates a shift in focus from what we should be doing - to fixing CSS bugs. It is not hard to create a simple XHTML/CSS/EcmaScript based blog. But when it gets more advanced than that, CSS bugs and browser differences makes the cross-browser dream seem far away. That said, I am confident that we will support more browsers in the future as browser bugs are fixed and standard support is getting better.
Check out the Acid2 test in various browsers. They ALL are incapable of rendering a correct result of the page.
If you are using Internet Explorer 6.0 then check out the test drive of 24SevenOffice. Click on 'CRM' in the menu and then 'Customer Relationship Management' to see the CRM module.