I have an office with a door and I love it (but no windows to the outside, unfortunately). If I'm on a call or just want to be able to work uninterrupted for a while, I'll close it, otherwise I'll leave it ajar so colleagues can stop by if they have a question or want a quick chat. I work in product R&D; the building also has a cube farm area for IT and HR and business folks, so I'm really happy I'm not there.

My team is distributed around the world so my team collaboration is all virtual, although my management and some of my [internal] customers are located in the same building as me so they can stop by my office or vice versa if we have things to work on together.