I visited Potsdam twice in the summers of 2006 and 2007 and was surprised by how much reconstruction had been carried out in the meanwhile. Post-Communist Potsdam is now becoming the beautiful wealthy looking city it used to be before WWII. Except the justifiably most well known of Potsdam's attractions, namely Sans Souci Palace and park, the area is loaded with interesting sites to visit. Don't miss Alexandrowska - the Russian colony errected in the 19th Century for Russian settlers, which is covered by the Unesco title. It offers lovely traditional Russian wooden houses in ornated style. A small museum, though not very interesting for itself, offers you a glimpse into the interior of these traditional houses (www.alexandrowska.de).
Another lovely district covered by the Unesco title is the Dutch quarter which was constructed for Dutch merchants and artisans in the 18th Century by the architect Jan Bouman, whose own house can be visited (Mittelstrasse 8).
At Cecilienhof Palace you can admire the original treaty which ended WWII signed at the famous Potsdam Conference in 1945.
Another tip - though unrelated to the Unesco inscription - is the filming area which used to be the most important one in Germany is still in use.
All in all, I recommend to dedicate more time to explore lovely Potsdam than the usual one day trips out of Berlin.