Is it true that Microsoft is doing two devs per office these days? I just thought back on all the places I sat at Microsoft and out of 9 different offices (ok, two were cubicles), I never shared once. They do make you move around a lot, obviously.
The trend when I left (4/13) was towards open offices
Internally, for teams that use offices, there is something known as the "pain index" which is the person/office ratio. As a rule of thumb, you might be expected to share an office upto about two years, and by about 5 years might expect to have a window office - but it was very dependent on team
[Edit - added pain index]