Singular or plural for enumerations?

Do you use singular or plural for enumerations? I think it makes best sense with plural in the declaration

enum Weekdays
{
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
}

... but I think it makes more sense with singular when using the type, e.g.

Weekday firstDayOfWeek = Weekday.Monday;

I read a recommendation somewhere to use singular whith regular enums and plural with flags, but I would like to hear some more pros and cons.

Here it is straight from Microsoft:

http://msdn.microsoft.com/en-us/library/4x252001(VS.71).aspx

Use a singular name for most Enum types, but use a plural name for Enum types that are bit fields.

One recommendation comes from the .NET Framework Design Guidelines, page 59-60:

Do use a singular type name for an enumeration, unless its values are bit fields.

public enum ConsoleColor {
  Black,
  Blue,
  Cyan,
  ...

Do use a plural type name for an enumeration with bit fields as values, also called a flags enum.

[Flags]
public enum ConsoleModifiers {
  Alt,
  Control,
  Shift
}

In the .NET Framework, most "normal" enums (e.g. DayOfWeek) have singular names and flag enums (e.g. StringSplitOptions, BindingFlags) have plural names. It makes sense, since a value of a flag enum can represent multiple items but for a non-flag enum, it can only represent a single item.