Cash Cow Franchise: A huge hit in Japan and overseas, to the extent that there are musicals and even concerts of them!
Defictionalization: Gakupo was based of voice samples from Gackt. Then Nico Nico held a vocaloid contest hosted by Gackt where they asked him to sing the winning songs Episode.0 and Paranoid doll. The result was Gackt not only created and released a remix of the song Episode.0. But he also created a video that was identical to the original Episode.0 pv but with the pictures of Gakupo replaced with pictures of Gackt dressed as Gakupo. Here is the original pv of Episode 0. And here's the Gackt version featuring Gackt dressed as Gakupo Episode 0 Gackt version.
Vocaloids themselves for Sharon Apple. Synthetic pop-star, human vocal element, live holographic concerts...
Fan Nickname: Among Brazilian fans, Maika is also called Maik„o ("Big Maika").
Miriam is Miriam Stockley (the voice of Karl Jenkins' Adiemus project)
No Export for You: Many of the non-English Vocaloids are rather difficult to get if you don't live in Japan, and shipping can get to ridiculous prices. Yamaha attempted to avert this with some Vocaloid3 banks such as VY1V3, Mew, Aoki Lapis, Tone Rion, and the V3 Gumi banks available as downloads, Voctro-Labs ships Bruno and Clara internationally, and SBS put up SeeU on eBay (albeit at a considerably higher price), but some, like Yuzuki Yukari, are still rather difficult to get overseas.
In addition: Do you want to buy an album by your favorite composer, or a compilation album? Unless it's registered on KarenT, you will probably never be able to get it, because they're usually sold at Comiket or VocaMas - and even if they're sold online too, they're usually on Japanese-only sites.
Even if you can read Japanese (or use a translator for your browser) good luck seeing any of the Theatrical Plays based on the more famous songs. Those few that do have DVD releases never seem to have subtitles, English or otherwise.
And then there's the licensed games, notably the Hatsune Miku Project Diva series, which were Japan exclusives until Project Diva f, which at least was made available in the Southeast Asia region, but that's it so far (and it's still in Japanese). There are hopes however for the latter to see international release, seeing as how an American promotional video for the PS Vita shown in Gamestops shows gameplay footage of that game.
Averted with Project Diva F for the PlayStation 3. After Sega posted on their Official Facebookpage the possibility of a western release of Project Diva F for the PS3 if they get enough likes and shares (a stunt similar to what Crypton did for Miku's English voicebank), they eventually met their target and subsequently announced the release of the localized version of the game in the US and Europe, eventually released on August 27, 2013.
But the special mention goes to the another Miku x SEGA game, Project mirai for the 3DS (It's Nintendo's Project Diva with Nendoroid-ified Vocaloid! Kawaii!). The game's never released outside Japan, both prequel and sequel. Meaning you'll never play them if you don't own a Japanese 3DS. And yes, the fans are begging for their lives for the localization.
Actually, Yamaha updated en.vocaloidstore.com (where they sell Vocaloids), and they now sell packaged versions of SeeU, Tone Rion, MEW, Aoki Lapis, and other Vocaloids to North America and Europe!