The Metro system in Paris is awesome! You can get pretty much anywhere on 3 trains or less. My hotel was at the end of Line 8, at Lourmel station, and I could get to the opposite end of the city in half an hour. Plus everyone is very polite!
They offer a Paris Visite Pass which is a 1-5 day pass good for all Metro, RER, and many others transportation devices including to and from the airport. I bought one for 5 days at 60 Euros (zones 1-5), at the airport. The pass is very easy to use (1 ticket for everything), but is quite expensive. I should have bought the much more affordable ticket that was zones 1-3, which is all of the Paris city center. The other zones go to the airports, Versailles and other areas outside of the city.On my sixth and seventh days, I simply bough individual tickets at a price of 1.80 Euro (and an 8 Euro ticket to the airport). I think next time I will buy tickets individually (or in books of 10), or possibly the Paris Visit Pass zones 1-3. More info can be found here.
My lodgings, the Hôtel Mon rêve Amadeus, were not bad. The continental breakfast was included, although it only really consisted of coffee, tea, orange juice, bread, a croissant, yogurt, and corn flakes. The 7 Euro charge is not worth it! The room was of course small, but this is Paris after all. I didn't have much of a view, but was very near the Metro station Lourmel, on line 8. The staff was friendly, and most spoke english. Their website above lists some useful cultural differences that all travelers should know about tips, travel, weather, and dining.
It seems to me that having Euros before getting to your hotel is very important. I recommend exchanging money at your home airport, or at the Paris airport. Unsurprisingly, the people who work at the airport seem to be fairly grumpy--remember ALWAYS to be polite. Politeness is so ingrained in the French mind and language that it is crucial to always err on the side of politeness.
My favorite places were the cafés. I really liked the ease and availability of slowing down your day to enjoy a café au lait and croissant.
I enjoyed the crypt a great deal. It was very old, and very quiet.
The gardens are just great. The Jardin du Tuileries, Jardin des Plantes, and Buttes-Chaumont were all very nice.
I really likes walking around and exploring. Paris is a city where you can pick a random direction and find some really interesting (and old) buildings, or gardins, or markets.
Since it is almost certain that Robin and I will visit Paris int he fall, I figured that I would spend this trip going to places that Robin has less interest in. So I saved us some of the attractions for my visit with Robin, including going to the top of Eiffel Tower. Robin and I can have brunch up there or something. Also, we will visit the Louvre, which I only saw the outside of. A visit to the Arc de Triomphe is also likely, which I saw from across the street.
Of course we will have to visit a dozen or so Cafés, perhaps Les Deux Magots or Le Café des Flores. It would be nice to eat at a resaurant on the Champs-Elysées as well.
I didn't go on the tour of Sacre Coeur, but would like to go up into the dome and down into the crypt. I didn't visit the Ile St-Louis, and my book has a nice walking tour of it.
The Paris Museum Pass is great and I highly recommend it. You get to choose either a 2 day, 4 day, or 6 day pass. And for that number of (consecutive) days, the pass gets you free entry to 70+ museums and monuments in and around Paris. I bought a 4 day pass for 45 Euros, and used it at: George Pompidou Center, Conciergerie, Museum of the Middle Ages, Notre-Dame tower tour, Notre-Dame archeological crypt, Musée D'Orsay, and Sainte Chapelle. Here is a complete list of museums included, including the Louvre, Arc de Triomphe, and Versailles. Most of these exhibits cost between 5-8 Euros, so the money came out about even. One of the best parts of this pass is not just it's ease of use, but also you don't have to wait in line to buy tickets. I skipped an hour long line at the Musée D'Orsay and walked right in! Please note that they just changed from 1/3/5 day passes to 2/4/6 day passes. More info can be found here. The only problem is finding a place that sells them. Some of the smaller monuments and museums sell them (the ones I saw were sold out). I bought mine at the Paris Tourist Office (25 Rue des Pyramides), which is near the Pyramides metro stop.
I was very pleased with my Eyewitness Travel Paris Guide Book. Although pricey, the photos inside it are great.