It's a shame people only get meaningful academic credit for creating new knowledge (regardless of its importance), and not for explaining existing knowledge better than anyone has before. For example, have a look at Neil Brown's "Ghost of Unix Past" series, or almost anything from the SysAdvent blog (such as Adam Fletcher's look at what really happens when you run 'ls'). If things like this were counted toward promotion and tenure, I think there'd be a lot more of them, but how to count is a hard problem. As Titus Brown recently posted on his blog:
This is the problem with the online world for scientists: there's no real systematized incentive to any of this online stuff. And that makes it really tough. I'm going through Reappointment right now...Nowhere on there is there a place for "influential blog posts"---how would you measure that, anyway?