TDE is a great new feature, but so is backup compression and using TDE essentially nullifies the other out. Try both together and see for yourself, although this is not recommended. Encrypted data compresses significantly less than equivalent unencrypted data. If TDE is used to encrypt a database, backup compression will not be able to significantly compress the backup storage. So, Mickeysoft gaves us two great new features in SQL 2008 we really can't use together. Also, please do keep in mind when using TDE that TEMPDB is automatically encrypted when you enable TDE on any database on a server instance and this can cause performance issues with non-encrypted databases using TEMPDB on that server.:-D