I tried it out and wasn't impressed. It was a buggy mess when I tried to log in to my work email (Microsoft Outlook Web Access... which you'd naturally infer would work with a Microsoft browser) to send out a recruitment exam that I needed to turn in ASAP to be eligible for an interview for a new job. It took me forever and I nearly tore my hair out.
Yes, email is IE 9 ultimate fail... as well as web sites you have to log into. Anything you have to jump firewalls and security and vpns and corporate (and other networks)... full of fail!
Not everyone will have these problems... it takes the right combination of 'incompatibles' to fail. The problem is, as everyone is tightening their internet exposure, this is going to happen more often.