Originally Posted by Aviatrix
but you will always find a seat in first class. (At least in my experience)
I have used ICEs many times, sometimes on Friday afternoons. I think you definitely need a reservation on Friday afternoons (and other peak hours), even in First Class. The few remaining seats in the Bistro car are also quickly taken over by passengers. I have seen people standing in First Class from Frankfurt to Mannheim, Hannover to Hamburg. It is not pleasant; 3 euros is worth it, IMHO.