From Some Bozo: "I'd say the 20 € you save aren't worth it, just go with the standard ticket."
The difference between the savings fare and the normal ticket, is that with the savings fare, you are limited to traveling on a specific train, at a specific time. With a normal ticket, if you arrive early, you can get on an earlier train. If you're late, you can get on a later train. I've found that the special fares can be as much as 50 euro less, and are worth purchasing. If you think you are going to be going to Germany a lot, you can buy discount cards that will allow you to get 25% or 50% off of any ticket.
Another Bahn tip: if there is a specific public transportation stop you need in Nuernberg/Nuremburg, then set that as your final address as part of your train ticket. That extra bus/subway/whatever ride will actually be free if you set it as your Bahn.de end address, whereas if you get off the train and on to other public transportation, you will have to pay extra for it.
Word of warning for the main Frankfurt train station (not the one in the airport): as soon as you step outside, you are in a red light district. Sadly, there aren't any cheap food choices there, either.
Also, there are few things that make Germans more upset than simply speaking English to them. Ask first, in German, if they can speak English, before proceeding.
To a certain extent, public transportation is on the honor system. Make sure you validate your public transportation tickets. Plainclothes officers will get on the transport and check everyone's tickets after the doors are closed. If you haven't validated your ticket or haven't paid, then you have an automatic 40 euro ticket. If you don't have the cash on you, then they will take you to an ATM.
thousands of km racked up on the Deutsche Bahn and public transportation