I've also seen this, using both IE9 and Chrome, request to smooth.ch9.ms for any videos returns a 503 Service unavailable.

 

GET http://smooth.ch9.ms/ch9/c162/ff8aa905-66ec-497e-aebb-9eb60127c162/TheXNAshowAnimation.ism/manifest HTTP/1.1
Accept: */*
Referer: http://channel9.msdn.com/scripts/Channel9.xap?v=1.5
Accept-Language: en-US
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Host: smooth.ch9.ms
DNT: 1
Connection: Keep-Alive

HTTP/1.1 503 Service Unavailable
Content-Type: text/html; charset=us-ascii
Server: Microsoft-HTTPAPI/2.0
Date: Tue, 26 Apr 2011 14:24:31 GMT
Content-Length: 326
Connection: keep-alive

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd">
<HTML><HEAD><TITLE>Service Unavailable</TITLE>
<META HTTP-EQUIV="Content-Type" Content="text/html; charset=us-ascii"></HEAD>
<BODY><h2>Service Unavailable</h2>
<hr><p>HTTP Error 503. The service is unavailable.</p>
</BODY></HTML>