I'm not sure. I tend to hear so many different things from the Europenas I talk to (probably because I talk to so many).
My Polish friend told me flying tends to be the absolute cheapest, so unless interailing can beat flying, I doubt I'll do it as I'm pinching pennies as hard as I can on this ice breaker Euro trip.
And an update, it looks like I'll be spending some time in Munich in mid-May, and on the Polish coast near Gdansk in June.
After that I want to hit up Tokyo and stay for a long while. Like as in live there...