This may be less making hay while the sun shines than a mountain out of a molehill but I want to mention this as an important part to this post to start off, this is something I recently saw: http://www.cracked.com/video_18775_8-mind-blowing-connections-between-works-joss-whedon.html
Because they missed some big ones between Roseanne (which is hardly a surprise, despite having major and minor links between the two shows like Alyson Hannigan in a walk on to Glenn Quinn being a major character in Angel) and the Buffyverse. Even with their attempt to start off and take things further in a single vein I have noted a similar theory before. I even have a name for this theory:
The Harris theory.
The basic idea is simple: Jackie Harris and Xander Harris are cousins. Admittedly distant in all probability, still. Markedly then Roseanne Conner and the Conner children, whose maiden name would have to have been Harris is also part of the family. If true this means the Buffyverse is _in_ the Roseanne Universe (because Roseanne predated Buffy). Add in to that the other works, if the Cracked After Hours team are correct… this means everyone else is in the Roseanne Universe!
The thing about scientific theories is that they must be tested then peer reviewed, otherwise they are just cute little anecdotes. Here are some things that might lend themselves in the support of this theory:
Jackie and Xander Harris: there are links both large and small ranging from a short speech they both give that is nearly identical, to their roles (Supporting the main female character) and even to their weakness (both suffered or were supposed to suffer career ending back injuries) and liking (ok, bumping uglies) with a lot of people who are “bad” for them (though to be fair nearly everyone in Buffy seems to have that issue…).
Next up though is….
Conner & Conner
Becky Conner I & II: Two different actresses have played the role of Becky Conner and supposedly no one noticed. The Buffy Universe however provides an explanation: Magic, worldwide magic has implications and ping! Problem solved. The change that was mentioned comically later on in the series (with a nod to the same thing happening in Bewitched) suddenly makes a great deal of horrifyingly awesome sense, if this is part of the introduction to the Wheadonverse.
The real thing that seals the deal for me is Xanders Wedding (Episode 16 of Season 6, Hell’s Bell’s): Though related to Xanders own file think on this: When he talks about his family, which is often implied but real communication about is rare, and here it that family is stated to be as bad if not worse than deamons. Similarly the Harris Girls childhood was not exactly idyllic since just like Xander they had an abusive (and/or drunk) for a father.