http://news.ycombinator.com/threads?id=azrealus
I should clarify: accounts with this usage pattern seem to be common practice for spammers, that have been discussed on HN before.
azrealus, if you are a real person, I apologize for jumping to conclusions. I certainly have no problem with a real person, usage frequency isn't important - although it is preferable to contribute something to the discussion more than "I agree", since an upvote signals that.
I'll never doubt your existence again. :-)
Edit: I've thought about this a bit, and I think it's wrong to suspect users in this way. There are likely many who just vote on stories and don't feel the need to leave comments. Maybe the commenter is just getting their feet wet...