Most philosophers, I suspect, doubt that blogs are a good medium for philosophy. Even Brian Leiter --
the blogosphere a bit too ephemeral, and its attention-span too short, to feel like it is the right forum for serious philosophical writing (TPM).
-- not to mention your average tenured tweedy grayhair!
To Leiter's objection: Face-to-face conversation is even more ephemeral and wandering, but it is an excellent medium for philosophy. Consider Socrates!
The blog is intermediate in duration, formality, and interactivity between philosophical conversation and published articles. It would be odd if the two extremes were suitable for philosophy but not the middle; I see no reason to think so. Now, of course, many blog posts are bad -- as are many philosophical conversations and formal essays. The reasons for this are obvious and have nothing to do with the medium.
Different media differently balance virtues and tolerate vices. Blogging has one virtue that I've come to think very important to philosophy: It forces you to distill an idea to a clear, communicable core.
I'm increasingly suspicious of incomprehensible, "difficult" philosophy. The human mind, when facing abstractions, can barely deal with "unless X, not Y", much less page after page of Hegel. If you build your philosophy on a tower of technical concepts and complex arguments, it will topple with a poke. By being insufficiently clear, you can avoid decisive refutation (see my post on "profound" philosophy); but the way of integrity is to make each piece plain and simple, able to stand on its own. Posting your thoughts on a blog -- that is, making your thoughts brief and comprehensible to a general audience who may not have read previous posts -- is thus a form of intellectual discipline.
Some more specific advice to fellow philosophy bloggers. (This advice applies only to posts, not to comments.)
* Post only on matters to which you've given considerable thought. If you're a leading expert on X, your reflections on X are much more likely to be worth something than are miscellaneous ramblings on matters that have left no deep tracks in your mind.
* Write to entice the reader. The title invites the reader to consider a topic. If the title is inviting, you have the reader for about two sentences; things had better be cooking.
* If a post takes more than two minutes to read or confuses the reader with jargon or complexity, then reading it becomes a project, rather than a casual pleasure. Few readers will continue.
* Each post should have at least one thing novel, of interest to the specialist. If you write outside your area of expertise, it is difficult to judge whether you are only saying what is obvious to those more expert than you.
(Now if only I would follow all this excellent advice myself!)