Yikes, I wasn't expecting a something that large. I guess I assumed
rosemary would be like thyme - something bushy but small and controllable.

Depends on the climate. In California (San Jose, for example) they
grow hedges out of rosemary. Here in Washington, DC we struggle just
to get it to overwinter (although it can get to small shrub size if it
lives long enough, which I guess is largely a question of drainage).