There has been some confusion about the re-entering France or the Schengen Zone with the assistant visa. In the past, a carte de séjour or visa de retour was necessary in order to leave the Zone and come back in. However, the assistant visa is a multiple entry visa so that is all you need in order to travel!
The latest e-mail from Carolyn Collins at the embassy in D.C. clears this up:
Many of you responded to my last e-mail with questions about the rules for leaving France over winter break, and after looking into the situation some more, I would like to clarify and correct the information contained in my last message. This information does not apply to those of you who have already had your visas validated by the OFII, or for those of you who were able to get the "visa de retour" from your local Préfecture.
A number of you went to your local Préfecture after my e-mail to get the "visa de retour" and were told by the officials there that you no longer need to get this special stamp in your passport since the new visa rules allow assistants to enter France more than once. I checked with my contact at the visa service here in DC and he confirmed that this information about the new visa rules is correct. The assistant visa should be good for multiple entries into France and will remain valid for the entire length of your stay, thereby eliminating the need to get a "visa de retour". Having your visa validated by the OFII is apparently only an issue if you want to use the visa like a "carte de séjour" (to get the CAF, etc.) and should not affect your travel in and out of the country, so I apologize for any confusion and stress my last e-mail may have caused!
In short, your current assistant visa should allow you to travel over winter break without a problem, even if the OFII hasn't officially validated your visa yet. If you are still worried and want to be extra cautious when you travel, you can always bring along copies of your "arrêté de nomination" and/or any paperwork the OFII has sent you to show that you are legally employed in France and have taken the necessary steps to begin your registration with the OFII in the rare case where the border authorities ask questions.
The Christmas vacation begins soon for all zones (samedi 19 décembre 2009 - lundi 4 janvier 2010), so take advantage of your time off to travel. Here's the remaining vacation schedule for this school year:
Zone A: Caen, Clermont-Ferrand, Grenoble, Lyon, Montpellier, Nancy-Metz, Nantes, Rennes, Toulouse
Winter vacation: samedi 13 février 2010 - lundi 1er mars 2010
Spring vacation: samedi 10 avril 2010 - lundi 26 avril 2010
Zone B: Aix-Marseille, Amiens, Besançon, Dijon, Lille, Limoges, Nice, Orléans-Tours, Poitiers, Reims, Rouen, Strasbourg
Winter vacation: samedi 6 février 2010 - lundi 22 février 2010
Spring vacation: samedi 3 avril 2010 - lundi 19 avril 2010
Zone C: Bordeaux, Creteil, Paris, Versailles
Winter vacation: samedi 20 février 2010 - lundi 8 mars 2010
Spring vacation: samedi 17 avril 2010 - lundi 3 mai 2010
Remember that vacation begins after class on Saturday (if you have Saturday classes) and la rentrée is the Monday morning indicated. If you are teaching in a DOM-TOM, you will need to check your académie's website for their academic calendar.
And don't forget the jours fériés:
April 5th: Lundi de Pâques (this is already included in spring vacation for Zone B)
May 1st: Fête du Travail
May 8th: Victoire 1945
May 13th: Jeudi de l'Ascension
May 24th: Lundi de Pentecôte
