The process of migrating to Exadata isn't any different from migrating to a traditional 64-bit Linux installation doing RAC. Just like any migration, you need to go through a test run, and test your applications thoroughly before going live....especially if you're going from non-RAC to Exadata, or an older version of Oracle to Exadata. Most of the issues that I have seen in Exadata migrations were not due to Exadata itself, but common issues that come up on any database upgrade or migration to RAC.
Also, I highly recommend reading Expert Oracle Exadata, published by Apress. You can purchase it here: http://www.apress.com/9781430233923
Agreed , take this as if it were a windows to linux migration and do a trial run first. Ensure you budget a phases for performance tuning. Depennding on database size, acceptable downtime etc you can choose different methods of logical and physical migration.