Yes, DB's long-distance punctuality isn't fantastic, but you have to realise the long distances a lot of the trains cover - think CrossCountry in pre-Virgin days, the trains pass through so many pinch-points that it's often very difficult to make up time. I have found, it seems contrary to some posters here, that DB often still hold connections, I suppose it depends how late the first train is or how busy the station is and if the platform is needed by another train which would in turn be delayed. If you're that worried by it, as others have suggested, plan longer connections and if it's all on time then you've got time for a pint or two
And following my recent experience after touching down at Stansted (forty-five minutes sitting on the tarmac waiting for some steps so we could actually get off the plane, followed by a one-hour delay waiting for our luggage - ludicrous!), I'll be using the train (and ferry where convenient) to get to mainland Europe for the foreseeable future!