Hi,
I am in total agreement with the use of RMAN.
dd is a very time consuming way for copying and you will have great problem in backup and restoration.
secondly, dd is a high I/O intensive so the system performance will go down drastically.

RMAN once implemented will be easier to manage. You can create custon scripts for backup, restoration, incremental backups etc. There is a little extra effort initially but it helps in long term. You can attach RMAN to other third party tools like Legato, Veritas backup and automate the whole process of backup. I have been using RMAN for last 1.5 yrs and would prefer it over any other thing.
Thanks
Regards