If I knew the answer, I would bottle it and would be rich. (insert mad laugher)
Lacking a bullet proof answer, the following are my observations regarding this issue. A while ago I was the chief interviewer in my company, and I have had the chance to interview literally hundreds of people. My own conclusions match Joel from 2005. The good people are already employed elsewhere, and are likely to be happy there. If they aren't happy, they tend to have the connections to find a job based on their known skills and experience.
In other words, unless something like the bubble burst has happened, you aren't going to find the good people in your interviews. This means that you have to look elsewhere for that.
I know that this isn't widely applicable, but I am using this blog as a good way of finding good people. The audience who reads this blog is already highly self selecting, and likely to share the same conceptions as I do about many things. I had several client engagements that resulted from this blog, and the environment I was working with was significantly higher than the industry average.
From the other side, the one thing that I am absolutely against is the "get a new job, close the blog" mentality. I wanted to point out couple of friends who did that, but I just checked, and both of them are blogging, which I somehow missed :-(
Anyway, what I am trying to say is that online presence matters. I have several friends who never had a blog, and wouldn't consider opening one. The direct implication is that some of the smartest people I have worked with are only known through word of mouth. Real story, I was at a client site one, and was half way listening to a hallway conversation, waiting for a conference call, and I heard the following: "Did you hear how Muhammad* saved [big cellular provider]'s when their [not important now]".
Some people has taken my suggestion to heart, and opened a blog. It doesn't really matter what they are talking about, what is important is that they do. Creating interactions in the community, creating a name for themselves. Getting recognized. Reputation matter, and having access to someone's thought stream over time is incredibly valuable in trying to estimate their abilities.
In the end, however, there is really no substitute for working with someone to actually evaluate their skills (which is a transient thing) and their abilities (which tend to change far more slowly, and what I really care about). Any attempt to short circuit the process is going to end in tears.
* That is his real name, and I had the pleasure of having him as my boss for over two years. Sadly, he doesn't have a blog. And yes, this is my own gentle way of trying to get him one.