I don't think individual offices are good. People will spend more time away from their offices than in them, attempting to collaborate, then since it's a pain to go back in and out of their office, they'll end up just staying out of their office and socializing most of the time.
Pair offices are similarly bad simply because you end up stuck with somebody you probably don't know, and it requires you to form a close relationship, or keep an awkward distance. If you can't stand each other, it becomes unbearable.
It's been my experience that many open office plans are simply a sly way of saying that the company doesn't want to invest in sufficient space for their team or in a decent build-out of the space.
Of course there are many fine exceptions to this rule, but I've walked into a fairly large number of minimally finished floors, each of which were essentially sheet rock stuck around the support beams, and a few offices in the corner for the executives and maybe an open kitchen off to one side where the plumbing happened to have been. Nothing says, "We corral the cattle in this space" better than this kind of plan.
I have similar issues with cube farms, why not just build offices then? The flexibility that cubes supposedly gives in terms of adjusting layout are never really used. I've seen plenty of established companies with cube farms that haven't changed layout in 20 years. So now the employee has to deal with a cheap workspace, and an open roof that all sounds and distractions leaks into. It's half-assed privacy with half of the distractions of an open floor, at 3 times the cost.
The worst are the hybrids.
The half-height cubicle says "I'm not even going to pay for the material cost and decency of a full-height, and I'm going to pretend that it's important that you can pop your head over the top of your assigned cube."
The waist-height cube is the most ill-conceived abortion of office planning that I've ever encountered. They only provide a symbolic segregation of the employee's space, with all of the noise and distraction of a completely open plan. They say "see, I want you to have your own space, so I'm going to splurge and move you one step up from concrete floors and bare sheet rock, but I want to be sure I can micromanage everything you are doing by simply sneaking up behind you at any time."
If you haven't seen one of these abominations, here it is http://www.officefurnituresaver.com/images/steelcase%20conte...
edit actually this example is out of the depths of hell. It pretends to be an open plan, a group plan (see below) and a waist-height cube, but succeeds at none of them. Now there'll be a dozen groups, each fighting over each other to hear, and nothing getting done.
The best, in my opinion, are small group offices, where individual teams are assigned, their backs to each other, and a small conference table in the middle. The team can close the door to eliminate distractions, they can work together in pairs or small groups as needed and separate as needed. They don't need to screw around reserving conference rooms for group meetings and/or presentations. If done right, they'll have plenty of personal space, and not feel like somebody is about to come up behind them and choke them from behind throughout the day.
The only downside is that as teams grow and shrink, the teams tend to shift offices around alot, or parts of the team end up sitting elsewhere and never really integrate fully with the team. But it's by far the most productive arrangement I'm aware of.