_{Summarizing what we chatted about the other day…}

First, fixing plagiarized wikis is a good thing. Please keep it up.

However, that doesn't mean they all need to be replaced urgently. You've been doing a lot of them in quick succession. Pace yourself, take the time to write proper replacement text. If you don't know what the tag is about and can't tell from Wikipedia, ask others to chime in (the Ubuntu chat is pretty active).

Why I rejected some excerpts

Most of your suggestions are good, but not all of them. In particular, several of your excerpts are markedly worse than what you replaced.

Wireshark is a FOSS packet analyzer.

You replaced the opening sentence from the project description with the one from the Wikipedia article. I'm sure that was accidental, but this shows that you are somewhat overeager in your fight against plagiarism (more on this below). Your edit is bad because it eliminates the mention of networking, and it introduces “FOSS” which is obscure (most people don't know or care what this means) and useless (almost all Ubuntu software is FOSS, so it is only remarkable when software isn't FOSS).

IcedTea is a successful project to create a working, FOSS build environment for OpenJDK. It also adds functionality to OpenJDK, including a powerful web plugin. The icedtea packages in Ubuntu provide this Java browser plugin.

First, why “successful project”? This is the kind of wording that tends to make me reject as advertising blurb. Second, that's more information than is useful in an excerpt.

p7zip is a command line compression utility from the 7-Zip project.

This one isn't bad in itself, although “from the 7-Zip project” is too much information at this point (why would I care about the project name?). The old text included the information that 7zip utilities exist on other operating systems, which is useful information (many people convey archives between systems).

Sweet Home 3D is an interior design application for visualizing furniture placement. Items may be placed on a plan of a home, and then viewed in 3D to convey an idea of how a design under consideration may really look.

Again, too much text. The old version was terser and more readable.

Not everything that is not original is plagiarism

Plagiarism is when you claim to have written something that was actually written by somebody else. Tag wikis and excerpts are not normally shown with an author, so there is no strong claim that the person who contributed the text is the author of the text. In particular, it is perfectly acceptable to acknowledge the source not in the text itself, but only in the edit description.

Futhermore, there is no implicit claim of originality when writing a tag wiki (as opposed, say, to a research paper). This somewhat raises the bar for plagiarism, since a mere lack of visible acknowledgement is not a claim of originality and hence does not automatically constitute plagiarism.

Furthermore, a good excerpt is often a short, descriptive sentence. There are only so many ways to formulate the essential facts about a tag. As we saw earlier, you came up independently (I presume) with the first sentence of the Wikipedia article for Wireshark. Not everything that someone has said before is plagiarism.

Furthermore, project descriptions are intended to be disseminated and republished. They are advertising material. Many of them are not suitable for tag wikis because they are overly promotional or do not fit well in an Ubuntu context. But if you find one that is, feel free to copy it: you're doing good both by Ask Ubuntu and by the project.

Conclusion

Removing plagiarism is good, but don't go on a witch hunt. If you've found the ideal text for an excerpt, go ahead and write it. Do not put an acknowledgement in the excerpt itself, the edit comment or the tag wiki body is sufficient. The most important thing is to have useful content in tag wikis.