It depends.

In SSIS 2012 you have two ways of developing your packages:

* using the project deployment model (brand new and too much to explain in a forum post)

* using the package deployment model (same as in SSIS 2008, also known as legacy deployment model)

If you choose to go with the project deployment model, you'll have to do a lot of changes (no more package configurations for example), but there's an upgrade wizard. This deployment model is however - in my opinion - much better than the other one.

If you choose to stick with the package deployment model, you'll probably don't have to change much. (maybe update the script tasks/components, haven't tried that myself)