Peter made a post on the IE Team blog about HTML+Time. Some of the comments seem a little confused calling it proprietary, non-standard and in some cases new. As the article he refers to points out this is an implementation of SMIL2.0 from the W3C that has been present in IE for many years.
I do find it interesting that people make such assumptions without even looking at the article refered to :) One piece of this functionality that I do think is really useful is the ability to synch media and content. This is used on the .NET show to keep a transcript rolling in synch to the video.
Peter's post is part of work the team is doing looking at functionality IE currently supports and deciding what we should do around it in future versions. This doesn't distract from the commitment we have already made to continue improvements to CSS etc. in future versions of the product which is clearly going to continue to be a priority.