The scenario you describe is perfectly legal. A couple can do what the IRS calls "Gift Splitting" and give $26,000 to an individual. You could do this twice and one couple can give another couple $52,000 in a calendar year.
IRS Pub 950 (pdf):
If you or your spouse makes a gift to
a third party, the gift can be
considered as made one-half by you and
one-half by your spouse. This is known
as gift splitting. Both of you must
consent (agree) to split the gift. If
you do, you each can take the annual
exclusion for your part of the gift.
In 2009, gift splitting allows married
couples to give up to $26,000 to a
person without making a taxable gift.
If you split a gift you made, you must
file a gift tax return to show that
you and your spouse agree to use gift
splitting. You must file a Form 709
even if half of the split gift is less
than the annual exclusion.
Example. Harold and his wife,
Helen, agree to split the gifts that
they made during 2009. Harold gives
his nephew, George, $21,000, and Helen
gives her niece, Gina, $18,000.
Although each gift is more than the
annual exclusion ($13,000), by gift
splitting they can make these gifts
without making a taxable gift.
Harold's gift to George is treated as
one-half ($10,500) from Harold and
one-half ($10,500) from Helen. Helen's
gift to Gina is also treated as
one-half ($9,000) from Helen and
one-half ($9,000) from Harold. In each
case, because one-half of the split
gift is not more than the annual
exclusion, it is not a taxable gift.
However, each of them must file a gift