As usual I was lazy to do a proper study of how to prepare for the trip, but I did check out some c stuff browsing the internet for around 4-5 hrs in total to figure out the basics of traveling in Europe. If you want a quick conclusion after the real experience, jump to the travel by planes section below.
Travel by Trains
Based on previous discussion with various people, I had concluded that I needed Eurorail pass to have efficient travel, I did some research on eurorail and decided to go for a 15 days Euro Global youth pass. The plus points I saw were
1) Unlimited travel to around 15 countries for 15 consecutive days, alowing me to postpone my planning of travel to a further later time (laziness has no limits)
2) The cost difference to the 3 or 5 countries select pass 15 consecutive days pass was pretty small and then Open Source conference participation was going to re-imburse some part of my travel
3) The other pass was for 2 months period with 10/12/15 etc days of travel, I found it no too effective for my case (which as I talk below might now be always true).
The website and the terms and conditions book that you get with the pass leaves some doubts in you mind which I tried figuring out over the net but couldn't for e.g The book says having euro pass doesn't confirm you a seat, you need to reserve your seats by going to the ticket window or through the conductor before boarding the train.
As I traveled around I figure out most of these things. Much as I as I understand here is how you use the pass:
1) For most short distance trains, like 1-2 hrs of travel mostly intercity trains, you don't need reservation (this is pretty much mentioned in train timetable if you get one from raileurope)
2) For most trains more than 3 hrs reservation is needed. Most trains have two Seats and berths for a night journey you might rather take a berth than a seat. Now in both seats and berths there is class 1 and class 2. Like business and economy, I usual the price difference is similar up to 3 times, I always traveled by economy (so do most tourists).
Reservations is similar to buying a ticket, so you may end up in long queue which should be avoided because you bought the pass but no such luck. Believe me each customer ends up taking 5-6 minutes on an average for buying a ticket. One alternative however is that you to do the train conductor and ask him for reservation. This turns out to be slightly costlier than buying it on the ticket window but saves loads of your time. My train from Paris to Nice ville for e.g I had to go through this option and I got a berth reservation for 20 Euros, while the Seat was free or 5 Euros (I don't recall)
3) Many students in Italy traveled by just hopping on the train and then sitting on the side seats instead of compartment seats. These seats aren't numbered so if you have them, you can sit without any problems, but every time someone pass by the corridor you are required to stand up. Nevertheless these seats are sometimes the best way to watch the scenery outside and you don't need a reservation for them.
4) Now about reservation costs for most long journeys you pay around 15 Euros with the pass for a seat, the cost for a berth various between 20-3o Euros. As per my conclusion journeys across countries are usually costly. When I inquired ticket cost from Rome to Barcelona I was given the number 85 Euros (only option) with pass. The cost for a night train from Rome to Munich however was 9 Euros for seat and 27 for berth. I am not very sure if my tickets included the 18-25 age advantage or not, I somehow feel they didn't because someone told me later that berths were cheaper for them.
Travel by Planes (the more economic option)
Sometime during the middle of trip I was told that I wasn't traveling the most efficient way. I didn't really change it during the trip but It should be important for next one.
Train aren't really the cheapest transport mechanism planes are. Now if you go look at any flight cost on the travel websites they are pretty harsh like 600$ from Paris to Genoa or Milan, but turns out that there are indeed low-cost airlines which operate at unimaginably cheap rates like 30 Euros between most cities e.g Rome to Barcelona was 30 Euros. One of the most popular once is ryanair.com. I forgot the name of the other one.
Traveling by Ferries:
Some countries (Italy, Spain and Greece) are well connected by Ferries. I initially planned to use my Free Italy to Greece ferry offer with my eurorail pass but some friends told about their horrible experience with the same and I quickly decided to avoid it. Seemingly unless you take a cabin you are gonna hate this experience. Reserving a cabin is like 60 Euros. So you should figure out the cost clearly before planning. As per my friends "traveling for 14-22 hours amid high winds and cold breeze sitting on an not so comfortable seat isn't the best experience of your life".
Traveling within Cities
Most cities are very well connected by public transport like buses or Metros. Paris metro is probably pretty famous through the movies already. Venice is pretty well known to be connected by Ferries and buses where ever both of them run. Rome and Florence has great bus service, though I found it rather easier to walk around the whole city on foot. In fact, I went from Rome train station to Vatican city and came back walking involving around 2-3 hrs of real walking time. Most youth hostels are pretty close to the train stations. In fact except for Aloha hostel in Paris I don't remember taking public transport to any other youth hostel. Amsterdam's trams are pretty nice and useful for going across the city from train station if you don't like walking for 30-40 minutes oneway. In Paris, Munich and Amsterdam I took Sandeman's new Europe free city tours which are always by walking and which are a great way to explore the city with other travelers. In short:
Paris: Take a metro train pass for 7 Euros a day or walk around, renting a bike is option too.
Munich, Rome, Florence, Pisa: Walking around the city is easy.
Amsterdam: 1 Euro ticket goes active for 1 hour in any public transport, walking is easy too, many ppl rather rent bikes, as per my guide, be sure to look them carefully :)
Venice: The ferry pass was 12 Euros for 24 hours (IIRC) a good deal. You definitely need to take ferry for going around.