I found this website a few years back. I thought it could be useful for teaching kids, giving vices to characters. Some of the voice emulations are pretty good, and with melodyne cud be tweaked further. Unfortunately they've added a background sound to the demo. 
 
Maybe a melodic variant could stem from the same process sometime ckse in the future.
 
http://www.acapela-group.com/voices/demo/

The latest version seems like a much greater improvement over the last one.  Although I'm still not sure it's realistic sounding enough to use as a lead vocal.  But for backing vocals, with harmonies added, combining it with the entire mix of a song, I think it could be passable.   
It's nice to see that they are continuing to improve on this product.  For those of us that don't have great singing voices, maybe one day this can serve as a total replacement for main vocals.

Own V1-V4, bought the V5 standard package. To be brief: I'M SO HAPPY!
 
For Windows, you have to point your DAW at "C:\Program Files\Common Files\VST2." You can't choose where to install the editor/plugins, only the voicebanks. It also has experimental Rewire support, I think that wasn't possible in V3/V4 without an unofficial plugin.
 
If you have Cubase, Yamaha also throws in the previous V4 editor. V4 cross-synthesis (the ability to morph between two voicebanks) is gone in V5, but this way you can still use it.
 
Briefly tested it in SPLAT, the editor loads up and syncs with playback, yay!

BTW if you want to freeze Vocaloid's audio output, you have to put "bookend" events in its inserted MIDI track in Sonar: one note in the PRV before where the vocals start in the project timeline and one after they stop.  Then you hit the freeze button on the linked audio track.

Other observations:

The Cyber Songman, Amy, and Chris voicebanks have two phonemes that aid English pronunciation: [4], as in "bu[tt]er"; and [@l], as in "app[le]". They're not in the manual.

They brought back some stuff that's been missing since VOCALOID1!

• V1's icon palette is here as "Attack Release Effect." You can apply two expressions per note from choices like vocal fry, melisma, stops, etc., and dial the degree in.
• Parameter automation is drawn more like V1, with easily grabbable nodes. Changing the quantize grid also changes the resolution of node placement.
• They gave us back the Harmonics parameter! Now it's called "Exciter"! It's rad!

A lot of Japanese Vocaloids come with separate "power" and "soft" voicebanks, but I can see how the new synthesis parameters might reduce the need for multiples and cross-synthesis. Just one well-designed bank in the V5 editor could be "enough". That could be good for makers and users -- less time recording alternate voice samples, more time to pump out new characters, cheaper products, smaller downloads... Yamaha put a lot of thought into this version.

Leee

not sure it's realistic sounding enough to use as a lead vocal.  But for backing vocals, with harmonies added, combining it with the entire mix of a song, I think it could be passable.   
It's nice to see that they are continuing to improve on this product.  For those of us that don't have great singing voices, maybe one day this can serve as a total replacement for main vocals.

Agreed on not sounding real enough for lead work. But for harmonies and background vocals it would pass I think.

And I love to sing. But I have yet to find someone who loves to hear me sing! So I really had hope for this! LOL! :)

Maybe get in on the ground floor now to be able to upgrade for a decent price? But that's betting/hoping they continue development.

I haven't playing with anything like this, but am interested. I've watched demos of Realitone's Realivoxs. Are they the same kind of thing as this? How would they compare?

The 15-minute official walkthrough cclarry posted is a good introduction:
 
youtube.com/watch?v=UAtVGHl1AFM
 
ETA the manual: vocaloid.com/en/support/download/

Realivox is an "instrument," but better to consider Vocaloid as a synthesizer-sequencer -- a really complex one. It has automation lanes for a number of parameters simulating vocal characteristics: intensity, how open the mouth is, inflection between syllables, formant-shaping, breathiness, growling, and so on. You can have multiple tracks in the program itself, all loaded with different voicebanks. Unlike Realivox, you can type lyrics in plain English -- or Japanese, Chinese, Korean, or Spanish. Vocaloid will convert them into phonemes you can tweak to make the pronunciation more natural. It will even automatically split syllables across notes.

So while it's way more flexible than Realivox, it's always been harder and more time-consuming to achieve a performance-ready sound outside of backing "ah's" and "ooh's". Vocaloid5 is a huge step in the right direction, though.

The other historical issue with Vocaloid in the West is a dearth of voices provided by native English speakers, or voicetypes that an average musician here would find, um, usable. Yamaha's been working on that since v4 with Cyber Diva and Songman, plus there are the new V5 pack-in voicebanks. Third-party V4 banks Dex, Daina, and Ruby are native English as well.

OK, got it, I think. Realivox has sampled vowels and consonants that you play (via Kontakt). Vocaloid, as you say, is a synthesizer and sequencer of words and phrases. Thanks.

When does the Group Buy start?

Mesh
When does the Group Buy start?

I'm in if there is one 
 
Seriously though I have been waiting and waiting for a serious/usable version of Vocaloid to appear and V5 might just be it. I'm hovering on the buy button.