There's a difference between lifting someone else's Stack Overflow answer or blog post in its entirety and claiming it as their own, and copying an excerpt from a website into a tag wiki so that we can have a short summary of the technology. One of them is plagiarism, the other isn't.
The doctrine of Fair Use is relevant here. Copying an entire blog post is both plagiarism and a copyright violation; I don't think anyone will dispute that. But what about a site summary in a tag wiki? Does it qualify as Fair Use?
Let's review the criteria for Fair Use:
Purpose and Character -- Does the copied material seek to educate and inform, or is it meant to supplant the author's original work?
Nature of the Copied Work -- Are we stealing the guy's library, or merely displaying facts and ideas about it?
Amount and substantiality -- Are we copying vast swaths of the work, or only a tiny portion?
Effect upon work's value -- Are we diminishing the value of the author's work by publishing their summary in our Tag Wiki, or enhancing it?
I claim that short copies, like the one in the projekktor tag, satisfy all four of these criteria for fair use.
As I've already stated in the comments above, I think we should be cautious about discouraging people from filling in tag wikis. If the site owner was here, the way the projekktor tag wiki is filled in is exactly how I would like him to fill out the tag wiki. It's hard enough to get a good summary in these things (there are so many), and I'd hate for people to stop doing it because it's considered the equivalent of lifting someone else's answer and claiming it as their own. It isn't.
:(