Ask HN: How Much Spam is Acceptable? - A Spam Report Card

After seeing an announcement on Digg today about how they are working on their homepage spam problem (among other problems) I started thinking that perhaps Digg and I have different opinions of what is an "acceptable" amount of spam. (Link: http://about.digg.com/blog/yea-we-know-about-top-news-spam-and-some-good-news-too)

Then I realized that I still love twitter despite the large amounts of spam that exists there and tried to think of a social network or tool that didn't have it's users' experience negatively affected by spam significantly. After contemplating this for a while I thought I might make a list and grade the different social networks/tools that I use on a regular basis and see how others might grade them as well.

twitter: D+ Facebook: A- Reddit: A Digg: D- Skype: B+ outlook: B- Gmail: C+