Hey there.
We typically extract the data to a SQL database with the Database Accelerator Qdabra Database Accelerator Suite Version 2.0 - Developer
Then you can use SQL reports, Excel, or whatever you want to view and report on the data aggregated from all forms.
Otherwise you can merge forms, or promote properties and use SharePoint. Both of these methods can be somewhat limited depending on how you have structured your form.
Ideally if your form is fairly simple you could merge them all together but this is hard to control the final product as the XML is merged together across all forms and with the same format. In SharePoint, when you get a lot of forms, you will sometimes run into some issues.