All the cathedrals and museums start to blend together after a while, but you'll never forget the people you met and traveled with along the journey. The busiest backpacker season is from the May to September. If you're trying to follow the sun, try to hit the northern extremities during July and August. The Southern Mediterranean stays hot most of the year so this is a good place to be in the spring and fall. Backpacker transportation throughout Europe is great.
Trains are the preferred method of transportation for most backpackers while in Europe.
You can also get around by bus, and it's easier than going by train when going through Britain, Ireland, Greece, Portugal, and Turkey. Busabout doesn't compare to their Australian counterpart, but it's not a bad option as it relieves you of the headaches that can often stem from trying to figure out the train system in each new country. The problem with the Busabout is that they pigeonhole you into staying at certain hostels and it's not an off the beaten path experience like down under. Perhaps in a few years, their service will be more refined in Europe. The cost of traveling throughout Europe varies not only with the country, but also with the current exchange rate between the Euro and whatever your currency happens to be.