Kido Jou is not an all that popular character in Digimon. However, he does have his fans. Not only does he have his fans, his fans are very dedicated to him. For example, there are several (but not too many) sites that are almost completely devoted to Jou. Outside of those sites, however, he's somewhat hard to come by. Compare that to, say, Koushirou, who doesn't have a whole lot of sites dedicated to just him, but he is fairly often mentioned/drawn/etc in Digimon sites on the whole. Of course, then you have such characters as Taichi, who have a crapload of sites dedicated to just him, and is mentioned in just about every single Digimon website.
This pattern is not only found in websites, but in doujinshi, as well. My collection consists of several Jou only (meaning Jou, Gomamon, and perhaps a Kido brother or two) doujinshi, and I know of tons more that I want. For all that is holy I can not find any Koushirou only (again, meaning Koushirou and Tentomon) doujinshi. (All right, fine, I've seen one or two KoushirouXKabuterimon doujinshi, but I'm not going near those. >_<) Of course, in the general, all-character doujinshi I have, seems like there's more Koushirou in those than Jou.
This brings me to the third point: Jou is hardly paired up with anyone. Rarely is Jou in a shounen-ai pairing, but I have seen him paired with Yamato, a little bit with Iori, and a wee bit with Takeru. Honestly, however, YamatoXTakeru is a much more common pairing than YamatoXJou and JouXTakeru, and I've only seen a handful of JouXIori. I know of only 4 sites that are either JouXKoushirou friendly, or else just mention the pairing, and I have all of them bookmarked. (*sigh*) On the straight side, I've only seen a small handful of JouXMimi friendly sites, and I think I've seen a JouXSora one. Other than that, Jou is virtually ignored in the pairing world. Which means that the vast majority of Jou sites/doujinshi have just him, and are completely clean. (Damn)
Jou has his own fandom base, but outside of that base, he really is not all that popular. That fandom is very dedicated, however, and is not prone to pair him up with other members of the Digimon cast (which is probably a good thing). So, even though Jou is very much a minor character, I will still enjoy the Jou centered fansites, which feature some of the best art on the net. :)