DISCLAIMER: I make no claims about the correctness of any of the historical or geographical details in the following. In fact, if I don’t remember an important fact or date, I’ll most likely make one up. My memory is terrible and the trip was long so you should expect this to happen more often than not. Also, everything is from an American, and therefore biased, perspective.

About backpacking in Europe: if you haven’t done it yet, do it.
Make your plans. Quit your job. Take a month (or two or three!) off. Whatever it takes. Don’t wait. Don’t think, “Maybe next year...” Buy your ticket. Pack your bags. You won’t regret it.

You can use the navigation bar at the top to shortcut to your city of interest.

Here's a list of important topics that you can jump to:

Buying Plane Tickets - Consider open-jaw flights.
Packing Light - You gotta do it.
Foreign Money - Use your ATM card everywhere.
Guidebooks - Don't overdo it.
Language - Learn at least a couple phrases.
High-Impact Tourism - Don't participate.
Guerrilla Tourism - What's the point?
Other Travelers - Everyone you meet is your friend.

Or, continue and follow the tour start to end...