In my environment we are going from raw to mounted filesystems for ORACLE databases as we speak.
We are upgrading to 11.i and new hardware. from K-class & V-class to Superdome and Keystone systems. In addition, we are enabling largefiles that allow for larger than 2GB files. This will decrease the amount of table spaces needed for the large Databases that we will be creating, upto 10GB, and allow for more efficient storage of databases. Also, we are going to the new 170+GB disks for our EMC SAN which are more reliable than the current 80+ GB disks.
So the decrease in performance will be offset somewhat by the OS and hardware upgrades.
And the big PRO is that we can manage the filesystems with our backup utility, NetBackup, more effciently and with greater accuracy, instead of relying on my DBAs to remember to backup their databases.