Chrome also added special handling to work around poor browser sniffing in Hotmail, which is ironic because Opera had to do the same for Google Docs. Opera claims that most of what they have to deal with is actually improper browser sniffing on sites that didn't work in a previous version of Opera but work fine now. Looking at Microsoft's list of sites, it seems to be a similar story, many sites have IE-specific code that isn't necessary in IE9.
http://www.opera.com/docs/browserjs/
Chrome also added special handling to work around poor browser sniffing in Hotmail, which is ironic because Opera had to do the same for Google Docs. Opera claims that most of what they have to deal with is actually improper browser sniffing on sites that didn't work in a previous version of Opera but work fine now. Looking at Microsoft's list of sites, it seems to be a similar story, many sites have IE-specific code that isn't necessary in IE9.