Ad-hoc table type?

I was in a discussion with someone about the difference between ad-hoc
storage systems and SQL. Yes, I know, I was rolling my eyes as well. One
thing did strike me though was the idea that a table could contain a
variable number of columns.

Something like this:

create adhoc table foo ();

insert into foo (name, rank, serial) values ('joe', 'sargent', '42');

In an "ad-hoc" table type, when an insert is made, and a column is not
found, then a new varchar column is added.

I know the idea has a lot of holes, and is probably a bad idea, but it
answers an important problem of easily mapping programmatic types to a
database.

Anyone think its interesting?