You really only need to look as far as WoW. Their realization of bubbles is about perfect...BUT, it took them a while to get there.
It's fully toggle-able, and even when it's on, you only see bubbles from people in your immediate vicinity, and only from certain channels (/say and /party IIRC). The biggest problems are depth-ordering, what happens when they intersect, and how you handle bubbles that abutt the edge of the screen. Those are non-trivial issues and not everyone will agree with how they should be solved.
I'm wondering if those averse to the feature are imagining speech bubbles to infinity, with every NPC emote pasted up on the screen life graffiti? That's really not the way it will work.
Anyway, enough said on the subject.