The feature that adds meta keywords to the header of each page implementation of this feature is insufficient, and the very concept of selected keywords is ultimately flawed. It should be removed.
The idea of meta keywords was to provide search engines. From HTML 4.01 (http://www.w3.org/TR/REC-html40/struct/global.html#h-126.96.36.199):
A common use for META is to specify keywords that a search engine may use to improve the quality of search results.
"Some indexing engines look for META elements that define a comma-separated list of keywords/phrases ... Search engines may present these keywords as the result of a search."
So what's wrong? To start with, MediaWiki's implementation of this feature is worse than useless. If we are to believe it, the most relevant terms for Wikipedia's main page are:
"Main Page,1769,1945,1994,1999,2.5D,2004,2009,2D computer graphics,622,Aiea, Hawaii"
For the current featured article, they are:
"Domitian,Articles with unsourced statements from July 2009,Flavian Dynasty,The Triumph of Titus Alma Tadema.jpg,Special:Search/Domitian,69,79,81,96,Abdication,Abortion"
The theory is that these topics are important because they are either within the title, or linked in the article. This misses the point, as search engines _already look_ for text that is in the title or linked in the article.
As shown above, the algorithm fails spectacularly to select sensible keywords. These keywords would do more harm than good if they did anything. Fortunately, they do not. Modern search engines do not use these keywords because of their propensity for spam/SEO (see http://en.wikipedia.org/wiki/Keyword_stuffing). They simply cannot be relied on.
Google went out of its way to talk about every other meta tag, then denied using keywords when asked:
(John Mueller: 'You're right in that we generally ignore the contents of the "keywords" meta tag.')
Unfortunately, the 80-100 gzipped bytes (250-350 uncompressed bytes) these keywords occupy per response still negatively impacts users. Coming as they do before other headers, the keywords delay the load of linked CSS and JS files, as well as the content itself, occupy cache space, and take CPU to generate.
Providing a way to specify appropriate keywords is not a solution, as it would distract attention from actually useful editing. The standard itself has been abandoned by those intended to use it. This feature should be removed altogether, or at the very least made optional and turned off by default.
(Ironically, the meta keyword that *is* sometimes used - "description" - is not supported by MediaWiki, probably because search engines do a good enough job at figuring out appropriate text without it.)