When signing a card for instance:
Wishing you a Merry Christmas!
Love, The Sutherlands
Rich, Jane and Samantha 
OR
Love, The Sutherland's
Rich, Jane and Samantha

Howdy mjtjs-ga,

For the purposes of signing a card, you want to use the plural form of your
name, and not the possessive.

The Guide to Grammar and Writing, sponsored by the Capital Community College
Foundation, has a great example.
http://cctc2.commnet.edu/grammar/plurals.htm

"When a family name (a proper noun) is pluralized, we almost always simply
add an 's.' So we go to visit the Smiths, the Kennedys, the Grays, etc.
...
Do not form a family name plural by using an apostrophe; that device is
reserved for creating possessive forms."

For instance, you wouldn't write "We are the Sutherland's." but rather, "We
are the Sutherlands."

The JB Ink "Etiquette of signing your greeting card" has more examples.
http://www.jbink.com/signing.html

"Other acceptable forms are: 
...
The Joneses
Mary, John and George"

Note that in this last example, an "es" is added to the last name (Jones)
because it already ends in an "s," so as to avoid the awkward "Joness."

The best example of the use of an abbreviated possessive form of one's name
is on the front of a house, where you would use "The Sutherland's" so as to
show that the home is your possession; "The Sutherland's home."

So, you want to use the following on your cards.

Wishing you a Merry Christmas!
Love, The Sutherlands
Rich, Jane and Samantha 

If you need any clarification, feel free to ask.


Search strategy:

Google search on: plural grammar "The Smiths"
://www.google.com/search?q=plural+grammar+%22The+Smiths%22

Google search on: plural "signing cards"
://www.google.com/search?q=plural+%22signing+cards%22

Looking Forward, denco-ga - Google Answers Researcher

The answer posted above is correct, insofar as it answers your
question. However, as an English teacher, educated in North America,
based in Britain, I feel duty-bound to point out two problems within
it.

The first, briefly, is not an error so much as a matter of style.  I think 
Love,
Rich, Jane, and Samantha Sutherland
looks more real than
Love, The Sutherlands
Rich, Jane, Samantha

Secondly, and possibly coming under the category "too much
information", is my knee-jerk reaction to a common error repeated in
the advice cited for the sign on the front of a house.  It should be
The Sutherlands' Home
to show that the house belongs to, and is occupied by, more than one
person called Sutherland.  In English we use s' (s + apostrophe) to
indicate plural possession (one thing belonging to more than one
person).

If the residents wish to omit the word "home", they should also drop
the apostrophe.  Imagine labelling a workshop or kitchen so other
users know where to find things. You would put up a sign saying
(the) knives
(the word "the" is optional)
to show where the knives are to be found.  Likewise the house sign should say
The Sunderlands
to show that they live in this place.

I have been accused of pedantry on this issue, but no arguments have
swayed my logic.  (And yes, I do have a sense of humour!)

Howdy brainybabe-ga,

The first point is not a matter of style, but rather a matter of
preference.  What looks "more real" to you might not to others.

To the second point, language is not static.  I would argue that
the use of "The Smith's" is now so well established in the United
States that it has become acceptable for use in the U.S.

Looking Forward, denco-ga - Google Answers Researcher

Denco, sorry to disagree, but my reaction to your comment is so
violent that it is probably a good thing we can't apply any special
effects to our text in GA.  I would be going for multicolor boldface
in size XXL with flashing lights, and I'd throw in some audio too if I
could.  Feel free to imagine the scream.

Ignorance may be well established in the U.S., but "The Smith's" is
not and never will be acceptable under any standard that reflects an
understanding of the basic forms of English.  No matter how many
aberrations of spelling and grammar and plain old malapropisms you
could identify as widespread, you are only establishing evidence of
rampant illiteracy and not proving acceptability.  What "The Smith's"
says is "property of the Smith."  And that is what it will still say
even if there's no one left in the U.S. who knows that.

I must agree with you, however, on the point that "more real" is not a
particularly apt criterion.  Even though a relationship in which you
sign yourself "Love" does not sound to me like a relationship in which
you identify yourself by your last name, how people express their
affectionate greetings to one another is certainly a matter of
preference.

Archae0pteryx