Using US electrical goods in Germany
The most obvious issue to consider when using US originated electrical goods in Germany is the difference in voltage and frequency of the mains.
Many items come with dual mode power supplies and have a discrete, hard to change by accident, switch somewhere on the back of the unit. This is certainly the case for most computer equipment and even some small items like hairdryers. Other equipment will actually be able to work on either system without adjustment. The small power adapters for notebook computers often work fine with anything from 100-250 V AC so then there is no real problem at all. The ones that are OK to use like that will carry a label on the power adapter that indicates as much.
If you want to use a device that is designed only for US voltages than you will need a stepdown transformer of some description. Such devices vary a lot in price and you need to work out what you need. The main difference is the power that each type of transformer can handle. More power means more size and weight and more money too. There is another issue though. Some of the very cheap units skimp on other areas and, as a result, you will find that they are not suitable for many uses. For example, a cheap transformer will probably be fine for your ice-cream maker but when you connect it up to your hi-fi, you find that you suddenly have a lot of mains hum in the system because of earthing issues.
That's about it as far as voltages go but there are also issues concerning the slight difference in frequency used for the mains current. Anything with a synchronous motor will run at a different speed. That is a big problem for high end record decks which often use such motors. It may also be a problem with other items like precision drills were you want an exact speed to get the best results. It can even cause a problem in that a motor running on 50Hz may be running outside its designed operating range. I have heard of problems with refrigerators either not working well or repeatedly blowing motors and these issues were eventually traced to the slow running speed caused by operating on 50Hz.
Signal issuesI'm sure that you know about the differences in television signals but what else is there?
Even the humble transistor radio can encounter compatibility problems. The channel spacing between stations in the US is not the same as in Europe. That is not a problem with radios tuned by an analogue dial but it can be a complete show-stopper with a digitally tuned radio that tunes by hopping from one channel to the next.
Anything that wants to transmit a radio signal is almost certainly out. This will include cordless phones, baby alarms, walkie talkies and radio controlled toys and models. The problem is that the frequencies used in the US are not always the same and if you happen to find that (for example) your baby alarm shares a frequency with German police radios then you will end up having to pay a very large fine.
Don't forget to read my pages about wiring and plugs and British electrical goods for a few more useful tips on this subject.