The vote is quite hard to do because it doesn't take in consideration preferences/ranking. So for myself :
Blog post is what I would more likely read, if pointed to. If it's on Less Wrong, since I check it regularly, I'll very likely see it, elsewhere... depends. The good thing of blog posts is comment, both writing them and reading them is useful.
Mailing list, page/static HTML : I used to read some mailing list, but I ended up just killing without reading the mails I get in them, so... if pointed to the archive I could read like a HTML page, but no more.
Academic paper : I could read it, but usually "big pdf" scares me, so I need to overcome this (quite irrational, I've to admit) initial reaction, so it requires the topic to really interest me.
Book chapter : I don't like e-books (especially DRM-loaded ones...) but I do read quite a lot of paper books. The problem is that I hardly will buy a book for just a chapter, so it means the other chapters have to interest me too, not just that one.
PowerPoint : I almost never open those, only when like to remember things I forgot about a talk I saw in a real-life conference. But I find the format very shallow as stand-alone document, it's ok as a support to make a talk, not by itself.
Audio file : requires lots of bandwidth (and my home bandwidth is saddly limited, since I'm far from the DSLAM), much harder to understand for me since English is not my native language, can't as easily stop reading for a while to ponder the idea, or re-read a part I didn't fully get, ... so the worse.
In our discussion of academic papers, Lukeprog argued that lots of smart people preferred to read ideas in academic paper format. Based on my observations, I mostly disagree. But that's just anecdotal evidence. Let's use Science!
Suppose someone at the Singularity Institute thought up a cool new idea: it could be about rationality, Friendly AI, decision theory, making money, or any of the other topics we discuss here on LW. Explaining it takes about ten pages, and it's nontechnical enough that it can be explained to a general audience of non-mathematicians. Which of the following explanations would you be most likely to actually sit down and read through?
EDIT: To state the obvious, this poll will be biased in favor of blog postings, since it's on a blog. However, I still think it'll provide data that's much better than anecdotal guessing. I've emailed a few rationalist mailing lists to try and counteract this effect.