1) Painfully slow compared to Instant's realtime. 2) Only one at at time. 3) Text. (People respond to visual cues, and for a vid site, better to have thumbnails display in the results with captions.)
I even ran into issues when Google automatically blocked my server for making too many repeated requests to the search suggestions endpoint.
However, I rewrote the site to query YouTube directly for search suggestions, eliminating the round-trip to my server. Now, all the magic happens in each visitor’s browser, so it’s faster and Google can’t block it.
I'm pretty sure they just want the person.
The real lesson here is for yourself and others here who think like you -- if you tell yourself that things like this take superhuman efforts, how will you ever be able to produce something creative yourself?
(Of course, everyone thinking that this is even remotely the same thing as Google Instant is also completely missing the real innovations in that product.)
edit2: had mentioned an error the site was having, but it appears to be fixed now.