Paris for 1 night (flight layover) - what to do?

no you can not store luggage in the airport. I belive you use to be able but not with the new security. You can store it at a train station tho.

As for what to do I guess it depends on your interests.

I would say a quick tour, the eiffle tower, Arc de Triomphe are easy to see, especially if you chose not to go up the tower.
I say stop at Place de concord the fountains are beautiful.
I say stay in the Marais or the latin Quater area and see the Notre Dame and if possible St. Chappel the stained glass is beautiful.

I'd say stay in the Latin Quarter area, so you're more central to more attractions.
Considering your short trip and honeymoon/romantic theme, I'd suggest "soaking things in" vs. running sight to sight. Here's my list: Montmartre (maybe grab dinner here); do a sunset river cruise (Vedettes Pont Neuf are a little more intimate); grab a bottle of wine etc, head down the river to picnic under glow of the Eiffel Tower; head back to the Left Bank/Latin Qu area where into the late hours the cafes and streets are still buzzing - walk around and soak it in for as long as possible. The next morning, grab a croissant and coffee and sit by the river (my favorite spot was the park on the river side of Notre Dame); do the church if you like.

Since the time in Paris will be finale your honeymoon, you will want the time to be a great ending for your trip. First, I would plan on taking a taxi to and from the airport. This should prevent wasting a lot of time and lessen stress. Second, I would take an evening dinner cruise on the Seine. The lights of Paris are so beautiful, and you won't have to search for a restaurant! It would be very romantic. There are boats that leave from the base of the Eiffel Tower, and there are plenty of recommended (by RS) hotels in that area. Third, if you are in your hotel early and want some exercise, take a walk up Montmartre for a great daytime view of Paris. It's an easy trip from the Eiffel Tower area by Metro. Or you could walk to the the Arc d'Triomphe and stroll down the Champ Elysee, then head to the boat for the dinner cruise. It should be a great way to end your honeymoon - what could be more romantic than Paris!

Book a room at the Hotel Regina across the street from the Louvre, take the hop on/off bus and spend time at wherever sights you like, have dinner on a Seine cruise, walk around until you feet fall off, splurge on breakfast at a 5* hotel the next morning and back to the airport for your flight.

Wendy, I would pop into the Louve late in the day and possibly try to catch a few of the biggies (but don't walk too much). Or if you are not big on art, just stroll along the Seine --late in the day would be beautiful (and very romantic). Once night falls, you MUST NOT miss going to the Eiffel Tower. You must see the light show that plays every hour on the hour. You don't have to go up the tower -- just this is more than enough, though the view from the 2nd platform is sublime. (It is a hassle to get up there though -- crowded, so don't take the time if lines are long) Just walking under the tower is a fantastic experience. From there you can walk over to the rue Cler area where there are lots of good restaurants. I always go to Cafe du Marche -- which is a big Rick Steves' recommendation, and full of his fans -- but it's friendly, reasonable and has good food.

Voila!

More thoughts from me, after viewing earlier replies.
The Arch de Triomphe is fantastic, but I would skip walking down the Champse Elyses. You don't need to see another commercial district, with pretty non-descript stores on so short a stay. If you don't want to do any art museum, see Notre Dame (just outside is OK) and stroll the Ile de la Cite / St. Louis - this is right on the Seine and will fit right in with a river stroll -- lots to see along the way.
Montmartre is fun, but out of the way and if pressed for time I would not include -- see it when you return. I hope you will! I'm taking my 5th trip to Paris this September. Pick any Rick recommended hotel in the center of town or find one on your own in the 1, 2, 3, 4 arrondisments -- is my recommendation. be close to where you want to be - within walking distance. Might not want to mess with the metro.