The media is full-on with the articles and reports celebrating Supernatural's 100th episode. @SuperWiki has been doing a good job in tweeting the related links, for example here and here. Variety interviewed Kripke for one of the articles here, mentioning the below:
 

Then in season three, they added two new recurring characters: Ruby, a seemingly good demon, and Bela, a thief that specialized in "Supernatural" artifacts. But a human villain in the "Supernatural" universe didn't sit well with the fans, so Bela was sent to hell. Ruby, however, went on to play a pivotal role in the apocalyptic storyline that became most prominent in seasons four and five.

So. Other current burning misogyny, patriarchal, better-meta-ed issues aside:

1. There are no villains in SPN. Unless they are demon-hosted ones. How, limiting. That's a wasted opportunity in a larger sense than before, especially when this arc purportedly ends this season. I wouldn't put it pass them to be visited by wayward angels and demons (yawn) in the next season

2. In this universe, the fans are the gods. It's not bad in a way but I'd read fanfic for that. It's OK if show pisses me off. Amazingly, like now.

3. Hell seems to be the last stop for everyone but the Winchesters. Perhaps that's the reason for all things heavenly (and hellish) treating the Winchesters like tools in their living times.

4. Seriously, I miss the human females we have had on the show, especially Season 1's. They might be unsatisfying at times (and so do the lead men, as with all things) but they are more than ready to take on their part in their own lifesavings. I bet if we put them altogether, they'll talk about how they were fine for most parts, until the Winchesters came along.

5. I'm actually surprised that SPN got to 100. I used to watch X-Files full-on until Season 5 (because the rest are filler, really) and even then it was touch-and-go for some time. I don't foresee it going another 100 though, more for the leads' desire to do something else and the lack of plot. Still, the show did a good job for making this far, and for keeping us interested, with us fawning or whining.

Happy 100, show.