When creating a custom object you get the chance to "Allow reports", by clicking the checkbox. Can anyone tell me what the checkbox does, exactly? The reason I ask is because I have created some objects with the checkbox not checked, and I can still create custom report types for that object, so not checking the checkbox doesn't actually prevent the use of the object in reports.
If you check the "allow reports" box then they become available to report on without you needing to define a custom report type.
If you click on "New Report" you will find them in the section Other Reports, unless your object is master detail to a standard object in which case you will find them with in that standard objects section. For example "Accounts with My Reportable Objects"
If you deselect "allow reports", then the Object is removed from the list of standard report types available. If the object is the child in a master-detail relationship, and the child has allow reports enabled but the parent does not, then no standard report is available.