I hate open plan offices especially when they're shared across multiple work groups, functional areas (e.g. devs sharing with phone ad sales!), or even worse, companies.

I think the happy medium is some flexibility among telecommuting, private offices, group work areas (taking over a conference room, or something less formal), and informal mixing areas. There is no single office environment which is best for all tasks.

I'm at my most productive by telecommuting from home one day a week, and daily from 0600 to 1000 (not always on the main company project); then working in the office, meeting with clients outside, etc. from 1000 to 1800, and then whatever team building, client events, etc. from 1800 to 0000.