< meta http-equiv="X-UA-Compatible" content="IE=8" >
Google Web Toolkit support for Internet Explorer 9 is still in beta. So, you may be experiencing problems with your GWT apps (I know that I was). The answer is to put the tag listed above into the head of your landing page. This forces Trident (the Internet Explorer rendering engine) to process the page as v8 instead of v9.
I was really disappointed to have to do this to all of you using the new IE9. It finally has decent CSS3 support. So, you would have been able to see all of the rounded corners and drop shadows in the site design. But, I think it is more important for the site to function than it is to look pretty.