I'm not sure if this was actually implemented into Starcraft 1 but, I think I've seen my uncle actually select a whole row of gateways and then just press the hotkey for the dragoon and all of the selected gateways started to build a dragoon. I'm not sure if they have it or not but, will they have this feature for Starcraft 2? It is a pain to just select one building at a time and start building, it takes too much time as well. If this feature exists already, please tell me how to do it(without hax... or thirdparty)
Multiple building selection is already implemented in SC2. As for SC1, I don't think it can be done without hax or third party.
MBS doesn't work the way it's described in the first post. If you select a bunch of Gateways and push "Z", one random Gateway will make a Zealot. This is the kind of thing that gives MBS a bad name. If you want multiple units, you'll need to tap the keyboard several times. This does give you more control; hitting "Z, Z, I" gives you two Zealots and one Immortal (all coming out pretty much simultaneously).
It is stated, as far as i know, that all buildings will build the unit you choose, and not that you need to click multiple times. Thats the whole concept of MBS, and was already implented in WC3, so im sure when Blizzard says MBS, they know what it is.
I've read that somewhere as well. I've also seen a youtube video of a pro gamer using it like that - it was very powerful. MBS looks like a key new feature of SC2. You couldn't do it at all in SC1 it was one of the biggest bug bears.