I have a Google spreadsheet that has not been made public, but just available to anyone that has the access link. Though I can access the data in CSV format from my browser
Now I can answer questions, so I will leave it answered for good (pasting from my previous comment).
My problem was that I was not storing the cookie correctly. At the time, I was using a Python program to try to download this. This fixed the problem I was reporting:
# Cookie management
opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(CookieJar()))
csv_data = csv.reader(opener.open(url))