With new IE in market the web developer community has been in the danger of supporting another extra browser. Recently we have found our application is in problem with IE9. We have a client application that put some data in User Agent Post platform value in registry. From IE6 to IE8 the post platform value was passing from server to client in UserAgent. So basically we had put some value in UserAgent Post Platform in registry from a client application and from our web application we had found the value (as the post platform values are passed in User Agent from IE6 to IE8). But with IE the post platform values are not passed with User Agent automatically.
User Agent and Pre/Post Platform value
If you are interested on how the Pre and Post Platform values works with User Agent you can visit the MSDN link: http://msdn.microsoft.com/en-us/library/ms537503%28VS.85%29.aspx
IE9 introduces Default User Agent and Extended User Agent
In IE9 the user agent has been divided into two parts:
Default User Agent (UA): IE9 by default will not send the pre/post platform values from client to server. So if you have some values in client’s pre and post platform then your web site will not get those values (from pre and post platform) as IE9 will not pass those values to server. However IE6 to IE8 will work as usual (i.e., pass those pre and post platform values) .
How to get the Pre/Post platform vales IE9?
You can get more details on this on MSDN IE blog: http://blogs.msdn.com/b/ie/archive/2010/03/23/introducing-ie9-s-user-agent-string.aspx