There are so many thoughtful, intelligent comments in this thread, I am reluctant to add my own... but I'll force myself.
First, the idea that this may be a cultural thing only goes so far. Some cultural expectations are acceptable; others are not. In some cultures, widows were burned on their husbands' funeral pyres. Should we who are not of that culture, support or accept this? I don't believe so. Sensitivity to other cultures is fine, necessary in this connected world; but allowing this sensitivity to dictate what must be the culture at Perl Monks is not.
liverpole has done us a great service by bringing this to our attention. Plagiarism is a problem, not just because of any moral issues, but because it has legal repercussions for all those involved. If material is copyrighted, Perl Monks could be sued for copyright infringement (theoretically; the risk is probably very small). However, this is the sort of thing that needs to be considered.
One problem I see is that material taken from elsewhere may actually belong to the person who posts it here. It is possible for someone to use an different handle on a different newsgroup or Website. It would be unfortunate to punish someone for posting his or her own material in more than one place. And yet... how do we know it's theirs?
One possible solution is to edit suspicious nodes and add a line that says, "taken from <link to wherever>", or "Originally posted by <name> at <link>", or words to that effect. It would alert others to the possibility of fraud, without actually condemning them for it. Each Monk could decide for him/herself.
Another problem is that, although we now have several clear instances of copying, most likely we haven't even scratched the surface. The Internet is a big place, and all you have to do is make a few cosmetic changes, scramble the order of words a bit, and it's nearly impossible to find the original work. We likely are missing plenty of other stolen work. That being the case, I feel it is important to make it clear that plagiarism is not tolerated here, and also to make the penalty serious enough to give someone pause. The chances of getting caught are remote; the consequences should be more than a light slap on the wrist.
Removing XP and tagging stolen work is probably a good idea. I believe there may be a legal obligation to remove known plagiarized works, but IANAL, so don't quote me. Just keep that thought in mind.
I am inclined to block a miscreant from posting for a certain length of time, in those cases where there is no room for doubt. You misuse your privileges, you lose them for a while. They can still read; they can post anonymously and reap all the benefits of Perl Monks. They just won't get any XP, which I suppose is the main reason someone would plagiarize here.
Of course, anyone can create a new ID in moments, but so what? That would mean they'd have to start from scratch. If they want to play sock puppets by upvoting their own nodes from another account, let them. Chances are they'll still get busted eventually.
For nodes that aren't so clear, I suppose we need to let the community speak. Despite occasional glitches, the XP system does seem to have a regulating effect on what goes on here. It's not perfect, but it's pretty good.
Finally, liverpole, I definitely don't think you're blowing this out of proportion. We are a community. What our individual members do, reflects on all of us - more so, if we remain silent in the face of plagiarism or other misconduct.