I was adding links to a blog, when I came to the conundrum of longevity of internet sites. When linking, you have to judge more than the site content: you need to judge the link itself. It's a major deterrent for the reader when a link doesn't work. It's like a mis-cited example on a paper that causes the reader to lose trust in your assertions. Of course not everyone clicks all the links, but if they do, it could expose the entry as poorly cited or even worse...outdated.
For now, I can think of more pros than cons for linking to Wikipedia entries. First, Wikipedia is a major site that won't collapse anytime soon (at least not without you knowing). Where as smaller sites might close down or redesign the site without you knowing, skewing your links in the process. They'll be broken and they might go unnoticed for a long time.
Second, you want your readers to actually click and read the links. Most people appreciate organized cliff notes of a topic, so they can read up on it quickly and return to the original blog without embarking on a long off-site topical tangent (link to a complicated Astrophysics site? No thanks...). Of course, if your entry is referencing to a specific topical discourse you might want to use an "edu" site, but then make sure to check your links down the line. Because who knows how long till a professor will be replaced along with his school Web-space.
I'm not giving Wikipedia a 100% approval, but I do think its a reliable resource to inform your reader while keeping their attention. The only real problematic 'Con' I can think of is that the little sites are missing out on the SEO of having outsider links. It can be like shopping at Walmart, when your local grocery shop could use your support more.
On a future note, when Google creates a virtual library of all the books in the world, this could be a moot point. Certainly students won't have any excuses for not linking to the real sources.
