I'm spending 2 months in Germany later this summer, definitely bookmarking this. I will still probably end up taking the ICE a lot though, it's just faster and has less transfers.
I've been to Germany many times; ICE is always faster than a regional train with tons of transfers. I know Germans complain about it all the time, but it's usually very good. I've only had 1 major delay. I've had more S-Bahn delays than ICE.