Today at 12:30 PM CST, the "add comment" button stopped working on any Stack Exchange site for Internet Explorer 8. It cites a javascript error.
(Edit: I'm not using Compatibility Mode, and JavaScript is enabled.)
@MartijnPieters - I can only use IE8 at work. It has worked fine until today.
@Bart - Inherently, no, it is not SE/SO's problem, but it depends on whether or not they want to lose a large amount of users for the next couple of years.
@GSerg - What setup are you using? I'm using IE v. 8.0.7601.17514 on Windows 7 Enterprise SP1 64-bit on a Dell Latitude E6420.
Let me make this explicitly clear. The company for which I work, an exceedingly large company with many SE users, does not support any other browser besides IE8. This will not change for the next couple of years.
Error details