The downside is that collaboration can become a crutch. It will only hinder you when you need to do the kind of "nose to the grindstone" work that's often needed.
To me, the ideal working scenario includes a private working space for each person and a public space for when collaboration is needed.
I agree. The best working environment I ever had was private offices with soft seating areas at the rend of each hall. It was easy to collaborate with others and easy to get a quiet environment. You never felt like you were interrupting several other people if you went to ask a person a question. If you had to take a phone call to talk to deal with a private family issue or call a Dr or lawyer, you could just close your door. If you had to send a private email you didn't need to worry that others will see something they shouldn't see. Offices also had much more usable desk space than I have had in open office settings.
I can see why people like offices (except for Zuckerberg are there any CEOs who sit in an open floor plan?), where I work now, the only people who like the open office arrangement are the managers who naturally have private offices.