Taking the train is no longer the cheapest way to travel in between some European cities, especially when you factor in the cost of your vacation time and how long it takes for travel. For example, going from Paris to Rome on the train takes over 13 hours and costs over $250.
I got a ticket on Easy Jet between Rome and Paris for a little over 40E, which is approximately $60 and the flight took around two hours. Even with the pre-flight time going through airport security, I came out way ahead of train travel.
The trick with small regional carriers like Easy Jet and Ryannair is two-fold: (1) they fly in and out of outlying airports. I chose Easy Jet over Ryannair because Easy Jet flies out of Paris' Orly airport at the south of the city, instead of Beauvais, which is 50 kilometers north of the city. (2) The weight restrictions on luggage is VERY strict. I chose Easy Jet over Ryannair because their checked-luggage weight limit is 20 kg instead of 16 kg. Even if you pay extra for a second checked bag, it doesn't increase your weight limit (what it means is that you can pay an extra 7E to have two bags make up your 20 kg instead of one). If you go over your weight limit, it costs 9E per kg. (A kg. is 2.2 lbs.)
However, it all turned out well. I mailed two packages home with my spare clothing that I wasn't wearng and the few items I had purchased. By putting my laptop, its spare batteries and my textbooks in my carryon bag, my checked bag only weighed 17.5 kg.
The flight is no-frills, even more no-frills than Southwest Airlines. No free beverages or snacks - you pay for everything. In addition, they sold parfume, stuffed animals and various other items on the flight in order to make money. However, you can't beat it for getting from Point A to Point B in Europe in a fast and cheap manner.