I've use vocaloids for making sampling most of the time, it's great for making chords, pads, choir, ambiences/atmosphere etc, but for something like chop chop, stabs, plucky sound, i found out that vocaloid are much inferior to the voiceloid.
You can use voiceloid as a instrument sound by write some non-lexical lyrics like ぱー , お〜, ノロ, ピカ , コソ, なで, ペロ, バタ, ペロ etc.
And chop it, fade it, comp it and put it on your midi pad and have fun.
When I read about it online they talk about the evolution and history of them. They talk about which bands use what equipment. Or they'll mention how a given synthesizer was used to make a particular sound in a famous song. But I have no idea how to use one or how they're supposed to be used. Or why I might want to use one over another one.
I downloaded DeXed which emulates the DX7 (because of its ties to Miku ^^;). I played around with it, went through all the presets but otherwise didn't know how to make good use of it. (Although, it probably has too much of a retro sound for the music I'm wanting to make.) I'm also interested in non-keyboard synthesizers, but don't know much about them. (I will say that, while I like FM Tracker music, I'm not really interested in using one for my music. Though I wouldn't mind learning more about them.)
[If you want you can just point me to a good website that explains this kind of stuff.]