Using IsPersonAccount Field in Account Triggers

Great news! It looks like the IsPersonAccount field is always available for use in Apex triggers, without the need to retrieve the field values using SOQL!

The following test was used to reach this conclusion (in Winter '12):

1. Create a trigger that activates or fires before/after insert, before/after update and before/after delete.
2. Add code to the trigger to check every record in Trigger.new and in Trigger.old with the following assertion: System.assert(accountInTrigger.get('ispersonaccount') != null);
3. Create a test method to insert, update and then delete an Account.
4. Verify that the test passes.

Optionally, one can also use the following code in the trigger to take a deeper look at the basic information that's always available, depending on what caused the trigger to fire:

System.debug('Trigger.new = ' + Trigger.new);
System.debug('Trigger.old = ' + Trigger.old);