Its normal to have it lose pressure given enough time. If its just leaking back into the fuel tank its not much of an issue but if its leaking from your injectors that could be a nasty problem. You can hook a fuel pressure gauge to the schrader (sp?) valve and check from there or if you don't have one the free version is as follows:
Raise the fuel rail a few inches above the manifold, injectors included, and turn the key on...*tada!*
Its a good idea to place a paper towel under the injectors. This helps keep anything from falling into the engine and also makes it easier to determine which injector may be leaking.
Stuff got done.