There is another interesting food service-related discussion on the Portland Mercury blog about coffeehouses. Particularly the "homogeneous" and "daylit only" coffeehouse and bakery Crema.
I agree with the majority, if the coffeehouse is busy and you have come specifically to sit for a while with your coffee mug and food item, then yes, saving a seat is necessary. Beyond that it is not against any rules, spoken or unspoken.
Japan trip update (& Thanksgiving week hours)
4 weeks ago