The title is a bit misleading. document.getElementById actually does work in IE8, it just works differently than it did in previous versions. Previously (in IE8 Compatibility Mode and earlier), getElementById actually searched based on name and id. This means that lazy or ignorant developers might have gotten used to using name when they meant id….
I recently installed a new Windows 2003 server and right off the bat started doing the Windows Updates. Even with Service Pack 2 installed, this process takes a while. Normally it wouldn’t be a big deal, but after letting the updates run on automatic for a while… Internet Explorer blew up.