> but ambient chatter is wonderful

I respectfully disagree. Maybe it's OK if the chatter is indistinct and unintelligible, but if you're in an open plan office it's likely that some of the chatter is from your neighbors.

The only thing more distracting than a single conversation next to you is two separate nearby conversations next to you.

Fair enough - and I expect it probably varies by individual. I would strongly wager that I get more done at a coffee shop, or some place with a low buzz, than sitting alone at my house - as long as the conversation isn't directly at me. I do bring some high quality over ear headphones with me in case it gets temporarily loud though.

Basically I think that as long as the conversation is interspersed / mixed enough that I can't easily understand what people are talking about, then I think it's not thought disruptive, and even beneficial in that case - I agree when people are talking loud / clear enough that you are basically a third listener in their conversation that it can be less than ideal.