GetDate() is SQL Server, so it is a non option.

The default in a strongly typed dataset is a literal, not a programatic
value. You cannot use DateTime.Now or DateTime.Today for this value, as it
tries to insert the literal string "DateTime.Now" which is not a valid date.
Boom!

You can, conceivably set a literal default, like 1/1/1900, but you have to
watch this, as this value could end up munging up the validity of your data.

ANother option is allow nulls on the DataSet and have the update method with
the GetDate() default (or, better yet, the field in the database table). The
downside of this method is a data disconnect between initial creation and
save (the client app sees a "nothing" while the database has a datetime).

Another option is seeding the default when a new row is created. This can be
custom, or you can use one of the built in events to capture the creation.
This matches your initial state to the database when the update is called.

This is fairly unique to types like DateTime where the default has to be
dynamic.