We've been hiring like crazy here and have had to move some furniture out of the way to open up space for new folks.  I took this as an opportunity to improve the work environment.  Previously, our setup looked much like this:

We tore down those cube walls and assigned teams to sit together in pods of four.  Engineers, QA and Product Manager are all mixed in together.  Here's the result:

The environment is much more open and collaborative.  And, perhaps counterintuitively, it's quieter.  I suppose folks are more aware of each other and keep their voices down as a result.