Do it!!
We converted out front room into an office. We both need an office, and we were using the other spare bedroom (10 x 10), but we outgrew it. Hubby suggested using the front room (it was empty! We use the family room for TV and visitors), and well ... why not?
Sure it's a little strange for visitors to walk into the house and the first room they see is the office ... but it's our house and it's the way things "fit".