Germany is a great country for hitchhiking. Just make sure you get on the Autobahn!
In Germany there are no speed limits on many highways. So you might first want to try to get a ride with fast cars before asking truck drivers!
Border crossings: Germany is in Schengen treaty. So, in theory the borders are open. But in practice the German custom officers or sometimes police will start demonstrating the sad traditions of their country to you if you are walking or riding a train with a suitcase or backpack somewhere near the border areas. Specially if you are a long haired man or not aryan by race or not mainstream dressed. If you belong to these subhuman people, you can be 100 % sure of these searches if crossing the border from Switzerland. If coming in with a commuter train, they easily take you out of your train to search your belongings, while your train continues without you. Forget any compensation for your ticket. This is just to show that your place should be in a freight train. Some of them act very neutrally, some others behave like louts. No use to complain any higher authorities afterwords, you won´t receive any attention, specially if you write in any other language but German. However, despite German customs and some cops, you will find lots of very interesting and hospitable people in this big country.