Scott Isaac has posted an article some weeks ago why live.com  is slow or "What they learned building live.com ":
There is one more thing I recognized when playing around with live.com. If you click on the refresh icon to update a container showing RSS news your web browser (I tested with Internet Explorer) will be blocked. I didn't had a look inside, but I think the asynchronous call is missing there. So, live.com is not the best web site showing Atlas related developments. I hope Microsoft will show us real web applications that can be used everywhere, on every device,...
Update: Scott Guthrie tells us in a comment below that the slowness of live.com is not comming from the Atlas framework. RSS feeds xml parsing is one of the slow functions from live.com.