I have a similar issue in a custom theme, although I wouldn't call it hanging as you can continue to use the application - just the start page doesn't load properly.
First - it works OK in the new themes supplied with v3. But, in the custom theme, the startup microflow runs, does everything it's meant to do except load the final form In Content - it leaves the content blank. If I click the home shortcut in the title area, it loads correctly. There are no errors. If I enable break points and step through the startup microflow, all steps are completed, but the form is just not displayed...
Ohh - and this issue happens with multiple browsers, not just IE
Haven't encountered a similar issue so far. Are there any microflows you are calling or what kind of form are you opening? Or does it hang at login?