Strategy for storage on Mac Pro with SSD
I have been building out Mac Pros for a while with SSD for the boot, user accounts and all the apps that fit.

Placing the large user data that doesn't fit as well as large Apps on the magnetic storage has worked well as the system and user caches stay on the SSD. You absolutely want your code and build scratch / temp files / object files on SSD for speed reasons.

The simpler the better - I have been using software RAID to span the HDD so the users all see three volumes whether or not they have one drive partitioned, a mix of SSD/HDD or full SSD/HDD and external drives for data and/or TimeMachine.

Macintosh HD - SSD unless lower performance is OK.
Data - all the HDD striped (optional on non SSD macs)
Time Machine - internal if possible - external

On the fastest macs - we are thinking of striping 3 SSD as DATA - moving the Time Machine to external storage as buying large (teraByte) SSD is still a costly proposition.