Specific to Windows XP & Windows Vista using IE8 (expected Windows 7 IE8 also)
The problem occures when copying any text directly from a Word document (Office 2007 maybe other versions to), into a custom text editor field on a product. The setup has 3 custom editor fields on products and products in 3 different languages.
Inserting the text into any of the custom fields will result in a complete system lock-up, assigning 100% CPU rescouces to the IE process until the request to insert the text times out.
Inserting the same text to the teaser or description fields runs smoothly, with no problems.