Should I use raid 0 with my optibay drive?
As the saying goes: "The difference between RAID 1 and RAID 0 is that the zero stands for how many files you're going to have after a hard disk failure."

Putting your 320 GB hard drive and your 120 GB SSD will allow you to share the space in between the two drives, but the risk in doing so is that you may have a failure at some point that makes your data unrecoverable. 

If you want to set up your hard drives in a RAID 0, I would recommend also setting up a backup solution that regularly backs up your files to a location that is outside of your laptop. That makes sure that your data can be recovered in the event of a failure.