Looks like something is wrong on their end, because when NewsBlur includes their feed address in the user agent, they give this error:

>>> feedparser.parse(u, agent='NewsBlur Feed Fetcher - X subscribers - http://www.newsblur.com/site/355068/a-java-geek (Mozilla/5.0 (Maci

ntosh; Intel Mac OS X 10_7_1) AppleWebKit/534.48.3 (KHTML, like Gecko) Version/5.1 Safari/534.48.3)')

{'feed': {'summary': u'<h1>Not Acceptable</h1>\n<p>An appropriate representation of the requested resource /feed could not be found on this server.</p>\n<hr />\n<address>Apache Server at blog.frankel.ch Port 80</address>'}, 'status': 406, 'version': u'', 'encoding': u'iso-8859-1', 'bozo': 1, 'headers': {'date': 'Thu, 09 Apr 2015 18:58:47 GMT', 'content-length': '320', 'content-type': 'text/html; charset=iso-8859-1', 'connection': 'close', 'server': 'Apache'}, 'href': u'http://blog.frankel.ch/feed?_=1998', 'namespaces': {}, 'entries': [], 'bozo_exception': SAXParseException('mismatched tag',)}

And if I take out the 'http://www.newsblur.com/site/355068/a-java-geek' from the user agent, it works fine. I'll email them and let you know if I hear back.