One of our issues was Notes/History tabs and Opportunity/Products tabs hanging on page load. We weren't able to reproduce the issue on all workstations, but the particular version of IE I was using was customized using the IEAK. Apparently this happens on other workstations as well, but anyway...
We saw a Javascript error in sdata-client.js which was "object doesn't support this property or method" so I put the sdata-client-debug.js library in place and checked where the error was coming from. Looks like line 1816 (v7.5.4):
var contentType = response.getResponseHeader && response.getResponseHeader('Content-Type');
Turns out the null-check on response.getResponseHeader is the culprit. Seems like perfectly fine syntax, so I did some googling and found this article:
http://www.mail-archive.com/swfobject@googlegroups.com/msg02416.html
Basically, XMLHTTP in IE uses a COM+ bridge so objects may return "unknown" type, resulting in the above error. I changed it to this:
var contentType;
if (typeof(response.getResponseHeader) != 'undefined')
contentType = response.getResponseHeader('Content-Type');
Seems to do the trick.
