This question calls for a religious war.
I have no doubt it should be plural because...
- A table is a collection of rows.
- The SQL syntax becomes more natural -
SELECT * FROM Customers instead of SELECT * FROM Customer.
- The analogy to OOP - you have a class
Customer and a list or other collection of customers called Customers.
SELECT * FROM Customers AS Customer WHERE Customer.FirstName = 'John' - Customers refers to the whole table while Customer refers to the current row.
Negative things
One has to switch several times between singular and plural during the development. You may start with a conceptual model - for example an entity relationship model - where the natural choice is to name the entity Customer. From this model you generate a database and must pluralize the name to get the Customers table. Finally you pick your favourit O/R mapper and it has to singularize the name again to get a class named Customer.
If you have to do this manually because the tool is lacking support (for example EntityFramework prior to .NET 4.0) it might be a reasonable choice to keep the table names singular but therfore get a class Customer instead of Customers without changing it by hand.
