While it is the standard advise by all gurus and guru wannabe who steals this advise from the real gurus, that it is good blogging practise to reply to all your comments, I think this advise have been somewhat misunderstood by all those who have just started to make a foray into the blogosphere.
It is basic courtesy, we learned in school that if someone greets us, we should acknowledge that greeting with a reply or at least a smile. We will be deemed rude if we ignore the person that greeted us. Like wise, if someone made a nice comment in your blog, you should at least reply with a thank you. That is being polite, but the blogosphere is a different universe altogether and lots of comments are made just for the sake of leaving a comment for reasons only known to the commentator.
Some may want to make their presence felt. Some may want to take advantage of your “do-follow” policy. Some really just want you to visit their blogs in return. Of course then, there are some who have really finished reading your post from the first word till the last and have their opinions to state or air out. Do we need to reply to all of them? My opinion is no. We only have to reply when a question has been put forth by the commentator in relation to your post We only need to reply when a comment warrants a sensible reply like when the commentator is in doubt about certain things you wrote.
The comment may be a few paragraphs long, but if what is stated is not in conflict with what you if written and you need to clarify your stand, then there is no absolute necessityy to type in a silly reply like, “thanks for dropping by” or something to that nature, which will not only be an insult to that particular commentator, it might look bad on the blogger too.
A constructive comment will attract many constructive replies. Likewise, a constructive post will also attract many constructive comments. So it works like a well oiled wheel, turning round and round, until you see decades of comments on some more popular blogs. More than 50% are one liners just to grab the attention of the blogger or his readers and has noting to do with the post. You certainly won’t find that blogger going around thanking every body for those comments.
Many bloggers laments about their lack of comments, never once stopping and asking themselves if the article they have posted deserves any comments. If rubbish has been posted, there will, if there is any, only rubbish comments. So look at yourself first before starting to complain about the lack of comments.
Having said that, I sincerely feels that this blog do rate a little bit higher than “rubbish”, but I am not complaining too much about the almost non existent of comments simply because I know the visitors that comes here physically is minimal, though my feed readers is nearing the 100 mark, so there is nothing to fret over. A blog like The Blog Herald too don’t attract many comments either as compare to a blog like Problogger. Talking about the Blog Herald, there is an article that all those who can’t find anything to blog about should take a peek. It is an article by Lorelle, and if posted in Problogger.net, would have attracted at least 50 comments. As it is, there was zero comments on that post.
So what am I to worry about lack of comments in this blog.

Firstly, I think there is the consideration what kind of blog you are running. Say, a technology blog that feeds technological information may not have the need to reply to every comment that comes their way. On the other hand, if you are running a personal blog, by virtue of the name alone, it’s supposed to be personal.
When we talk about personal, you cannot leave out the human element. I know, commentators leave their comments for all kinds of reason. Some noble .. perhaps some not so. Honestly, a blogger would not know. But then too much suspicion and questioning of motive will just defeats the purpose of blogging and interacting with people.
I’ll only get suspicious when they ask me to buy insurance from them.
(No offense to the insurance agents out there.. it’s a joke)
I agree with Helen to a certain extent. I try to reply to all comments. Why? Perhaps because I will never know if the commentator would revisit and check if I replied and also, because I am not swamped with too many comments to reply to right now.
Helen, Pablo ( since you agree with helen)
comments like what you two wrote here warrants a reply or at least a thank you. It provokes and starts a conversation going, which is the whole purpose of blog comments in the first place. Thus the advise by experts to reply to comments. To keep the conversation alive.
It really depends on what kind of comments are we receiving. Normally, I don’t come across comments that says “I agree with you!” then full stop. When it comes by, I will reply to them as well. Maybe a small “Thank you” or provide additional talks on it.
Actually, I have a few commentators that are subscribed to the comments. This is a tip on choosing who to reply. When they have subscribed to your comments, this means that they are seeking a reply from you but some commentators out there are using sites like co.Comments to track the comments they have posted.