The button for the Activities RSS Feed on the Dashboard page does not return the RSS XML. I am using Chrome 21.0.1180.83 m on Win7. I have not tried this with a different browser. It will download a file with no extension named "activities". If you open this file in a text editor it does contain the RSS XML.
I am thinking that the problem is related to the new (new to me, I not been using Garmin Connect since April 2012) owner name. Not sure why Garmin Connect is not just using my login/account name.
[a target="_blank" id="rssButton" class="rssLink" title="Get your activities as an RSS feed" href="/feed/rss/activities?feedname=Garmin%20Connect%20-%20maltbyd-runs&owner=maltbyd-runs" data-bitly-type="bitly_hover_card"]