The patch came out in early February. As it's being slowly applied, it seems to have a cascade effect. So I'm sure that you'll have more login and form submission problems to deal with over time, among possibly other things - I see reports of TCP/IP and local networking problems as well. This supposes, of course, that you or your clients use some flavor of IE that has this patch applied or you operate any kind of high volume web site with users who have applied it to their IE browser. Let's take a wait and see approach, shall we? =)

p.s. Apparently, as was posted in a comment elsewhere in this thread, MS Passport uses some kind of XML login scheme that relies on basic authentication, which this particlar patch has rendered inoperable, at least at present.