OK, i think i have a good hint to help you find the problem :

 

I created the simple ASPX page you told me to create and the conclustion is interesting :  If i access this page inside my web application, i still get a delay after each character and if i type fast, it even looses characters.  If i access the page in a seperate explorer window, it works fine.   What's so different in my application ??   The simple page thet i show in my application is displayed inside an IFRAME dynamically created in the main page and there are other IFRAMES in the page to show other content or to serves as a hidden postback frame.  Is it possible that your Javascript is trying to locate the HTMLEditor element by ID by parsing the document in the TOP window of the browser so if this document is huge, that causes the problem ???