I put a lot of thought into my oltp server;
4 data channels (two 3200 smartarray controllers I think there's at least 4 dat channels, it's been awhile..),
1 going to OS array (RAID 1) and swap array (raid 0)
1 going to log files array (raid 1)
1 going to data array (raid5)
1 going to data array (raid5)
I seperate the more heavily used apps on the two data arrays. I played with creating data files for tables on one data array and creating data files for the indexes on the other- fun, but more work than it was worth. I hadn't thought about using RAID1 for the data volumes, I'm curious but it's too late now.