In fact, pgAdmin does appear to set the default correctly, however, boolean fields in the data grid default to false regardless of what value is set as the default in the schema. If you insert data using raw SQL, or some other interface it should do what you expect. I think this is one of those 'feature-not-bugs'. I'll add it to my list of things to look at to see if we can improve it.
Regards, Dave.
It seems there is a problem with pgAdmin III 1.2.2 using PostgreSQL 8.0.3 in Windows XP. I have a boolean field set as not null with default value of true. When I insert a record, the field value is set to false as the default. This does not happen in psql or with EMS PostgreSQL Manager, where the field is correctly set to true. So, this appears to be unique to pgAdmin and not a problem with PostgreSQL.