Zador; In my years designing / building all sorts of electronic circuits I have always used the datasheets as a reference starting point. I have also found out that in a lot of cases there can be improvements made, especially looking at voltage stability and noise suppression from voltage regulators. Yes, the datasheet recommends a electrolytic capacitor on the input and just a ceramic capacitor on the output.. However when you are looking at a load on a 7805 which will have a lot of higher frequency load changes, it is recommendable to use (preferably and low ESR) electrolytic cap on the output of the regulator.. It can prevent / solve strange issues.