Upvote, beacuse I see myself as a descent programmer and my github account has been idle for ages.
Not to mention that holding a full time job and my wanting to spend time with my wife and kid leave very little time to maintain a blog (which I don't) or contribute to OSS (as much as I can, but next to nothing compared to other readers of this site).
Github can sometimes be a lot of copy and paste from either other repos or Stack Overflow or tutorials and such. For blogs, many very talented developers don't have one (or don't keep it up to date), and so it's very difficult to determine and verify ability just from an online presence.
Eh. I still think GitHub can be useful, it just might take a little more time. Instead of simply scanning the list of projects, take a quick peak at the commit logs for a few of them. It should be pretty clear based on the workflow if it's just a copy & paste job, or if the developer is actually working.
Someone could certainly game that, but it's a stretch...
The vast majority of talented programmers neither have a github account, nor do they keep a programming blog.