If you are a blogger, no doubt you've read plenty of those helpful articles on building online communities, how to attract comments to your blog, how to manage comment discussions, etc. The aspect I'd like to highlight here is very simple: make it technically easy for people to comment (if you want them to comment).
I've been blogging for some years, and because I like reading certain blog posts and because I like it when people comment here, I make an effort to comment on a post on someone else's blog if I have enjoyed reading a post. I know that other bloggers are like me and like people to comment on their blogs. So I think it is worth bloggers paying a bit of thought to their readers and making it easy for them to comment. Here are some of my suggestions:
You don't need to have log in AND a spam catcher. Anyone who can get through the log in is not a machine. If they are one of those "paid spammers" they will get through the captcha (or other spam catcher) anyway and plug their product.
Have a search box on your blog, high up enough for readers to find it without having to scroll down too much. Sometimes readers want to refer to one of your earlier posts on the same topic when they comment, and the best (sometimes only) way to find that post is via a search unique to your blog (not via the dreaded Technorati). There are lots of free Google search widgets out there (eg via Google itself or Widgetbox).
Check your settings in your blog dashboard so that it is easy for people to comment. Some blog platforms have defaults, eg only people with Google accounts can comment, anonymous comments are not allowed, only registered users can comment, etc. Check that these settings are as you want them, don't just leave settings at manufacturer's defaults.
Do a usability test every now and again: access your blog from a different computer from the one you usually use, and leave a test comment. Similarly, if you find it frustrating to comment on someone else's blog for a technical reason, or you think there may be a technical fault, the blogger will probably very much appreciate it if you drop them a line to tell them. People have done this favour for me before and I have been very grateful.
Nowadays, a lot of people are reading blogs in RSS readers, rather than at the blog itself, and click through to the blog only if they want to comment on a post. Services like the excellent Friend Feed are simple to use and have really, really great user interfaces that provide no barrier to comments and conversation among your group. It is much easier, technically, to read a blog post in an RSS reader, "share" it to Friend Feed and comment there, than to go to the blog and wade through the various thorns and thistles in order to comment on the post itself. I will always make an effort to comment at the blog if I read a post that interests me, because I know the blogger is likely to prefer that than a discussion of their post at Friend Feed or elsewhere, but the growth of these lovely-to-use "conversation platforms" is something that bloggers need to bear in mind!
There are some blogs on which I will not even attempt to comment, because I've had to provide a username and password, which the system doesn't remember from my previous visit and nor do I, also provide name/address details, and then go through spam filters. By which time I have forgotten what I was going to say, or it has stopped mattering. There are therefore strong incentives for bloggers to make their blogs as comment-friendly as is consistent with being spam free.