Agree with Ben and AC.
Sandboxing, plug-in support, updates via WSUS and GPO management makes IE a winner in the enterprise. Better management than the competition, users know it, has a big enough market share to ensure 99% of sites work in it and the security of it on Vista/7 with UAC IMHO puts it on par with the rest of the browsers out there.
Nothing against FF, Opera or Chrome (Safari is a different matter), but for enterprise deployments IE is in a league of it's own.
From a personal POV the alternatives don't add anything for me that I don't get with IE (use the IEPro plugin in IE8 on Win7), so I use that at home as well. (standard interface between home and work that way too)
Each to their own, but I think a few vocal people have their heads stuck in the sand. Windows is reliable, IE is secure* and Microsoft aren't that bad.
In the same way that Linux is usable, alternative browsers won't cause half the web to stop working for you and FOSS isn't the command line/only rough round the edges software it used to be.
This isn't 1999 anymore people!
IE is a perfectly reasonable choice now-a-days