Cologne has been doing it for a while, Trier is to follow from January 1st - It's called the accommodation or hotel tax. But to us travlers it really is no big deal. In early 2010 the liberal-conservative German federal government lowered the VAT on hotel accommodation from 19% to only 7% (for breakfast you're still paying 19% though). However the communities were missing that money and so they're now starting to charge an accommodation tax of 7-10% - so bottom line is you're not going to see any differences.
It will be no big deal if they include the tax in their stated price. It is one of things that I really liked about Germany for so many years, the absence of add-ons at the time of check out. I was sorry to see some hotels in popular tourist spots having a "Kurtax" in the fine print on their websites. Of course all of this should be very familiar to Americans, who pile on taxes at check out.