In Cape Town I used to enjoy going to some of the great Greek restaurants, and was always amused at the custom of smashing plates. (You can image how cool this seemed to me as a kid). Most of the restaurants would charge a small fee per plate you broke, and it was not too common to see people doing it, but rowdier parties and group celebrations would often end with ouzo, music, dancing and plate-smashing.
So, it is fairly interesting to note that in Seattle, not only are Greek restaurants less common than in SA, but plate-throwing is unheard of. It looks like the custom is on the way out everywhere. For example, in the UK restaurants have switched to less dangerous activities like tossing flowers, mainly to avoid the risk of injuries to customers and law-suits.
PS: You know you're in a Seattle Greek restaurant when you see salmon on the menu :-)