You can use a software like Scribe (
http://www.scribesoftware.com/) to migrate data between MS CRM and another system. It is easy to use and handles most issues that come with migrating data between systems. i.e. blank rows.
Scribe comes with connectors/adapters that handle blank records. It also comes with adapters for other systems like ACT, NAV etc..
If you write code to migrate data then you might need to code to handle exceptions.
Hope this helps.
H.
http://hassanhussain.wordpress.com/