I've received word that commenting may have been disabled on this Arduino blog... not sure what happened there, but I've made a change to the rules to allow registered users (and OpenID users) to post comments.
The old setting was "Anyone" and one day I woke up to find the same spam comment posted on every post in this blog... that's what forced me to change it to Google account users... that may have been the problem.
I hope this fixes the issue, and I apologize if anyone has posted comments that didn't make it... I'll watch this for a few days, but if a few readers reading this will try to post a simple comment to this post just so I can verify it's working, I'd appreciate it.
UPDATE: I got a lot of comments today so I think it's working again... I'm going to flip it over to accepting comments from EVERYONE (no special accounts needed) but I'm going to turn on moderation so I approve comments first... that way I don't wake up to 50 comments appearing from spammers! Thanks, all, for your understanding and patience as I worked this out.