I found a great list on the blog/news section for the ocPortal CMS, 10 IE compatibility problems that you might not have realised. While the post is related to ocPortal, the Internet Explorer compatibility issues likely will apply to any CMS viewed by the browser.
Over the year's ocProducts has maintained a private list of issues in different web browsers, and if there's one thing that is consistent it is that Internet Explorer has the majority of the problems. Sometimes they are bugs, but as you'll see from this list sometimes other browsers just do things better. I am writing this blog post not to bash Microsoft, but hopefully to provide some useful information to other web developers. Thankfully IE8 fixed a ton of problems, and I can't wait until we can ditch IE6 and IE7, but unfortunately this will inevitably be years away; never-the-less, as far as I am aware every problem here applies to IE8 as well as older versions.
I wouldn't be surprised if IE8 fixes some of the incompatibility issues that the author lists. I've been using IE8 at both home and work and have found the browser to be an improvement over IE6 and IE7. Nevertheless, I still prefer Firefox over Internet Explorer.
Now, the following rant isn't directed toward ocPortal but something that has hit a sore spot with me.

