This blog runs using the open source BlogEngine.net platform using ASP.Net 4.0. So far I have been pretty happy with the features provided overall, as it was pretty straight forward to set up and there are many themes/widgets.
The issue I had with using the out of the box comments system was seeing about 15 spams comments posted a day. I've seen some of the bigger blogs use Facebook Comments and they had less of the spammy junk, like ESPN in the screenshot below:
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