Upgrade to SQL Server from 2008 to 2012 - Developer perspective
Yes there may be impact. To start with, you must read


List of SQL Server features deprecated in SQL Server 2012
List of deprecated Database engine features in SQL Server 2012
Breaking changes to DB engine feature in SQL server 2012 


You must run SQL server 2012 upgrade advisor and generate report before doing migration. This report would list out all features deprecated and which would not work moving ahead in SQL Server 2012.

There is an option to allow few old features to work in SQL server 2012 and that would be by keeping compatibility level of database to 100 after migration. As a good practice you should change compatibility level of database to match that of Server. In case you want to change compatibiltity level please read Alter database Compatibility level. The good thing with compatibility level is it can be changed immediately if something goes wrong. About compatibility level please note that


  Compatibility level provides only partial backward compatibility with earlier versions of SQL Server. Use compatibility level as an interim migration aid to work around version differences in the behaviors that are controlled by the relevant compatibility-level setting. If existing SQL Server applications are affected by behavioral differences in SQL Server 2012, convert the application to work properly. 


For upgrading SSIS packages you should read BOL document I guess pretty much every thing is documented in Upgrade Integration services packages. If you want reference document please download 5 Tips on smooth SSIS upgrade to SQL Server 2012

Basically you have to read a lot and you have to look for features that has been deprecated. You might as well need to make changes in your code. As you can understand it wont be possible for me to tell you changes, you have to look at your code taking doc as refernce as do necessary changes.