What is proper etiquestte for a guest who is invited to a restaurant's grand opening?

* If you know the Proprietor then a gift would be appreciated, but not necessary. If you are simply an acquaintance then you were invited by the Proprietor to generate advertising for their restaurant so simply attending with a guest is appropriate enough. At the end of the evening be sure to let the Proprietor know you enjoyed yourself or, if you didn't, then say so and state your complaint as this will help the Proprietor to correct whatever is lacking in his/her restaurant.