New Boot Drive SSD ?

I'm looking to put a second HDD in my MacbookPro (2010 UniBody)..

It's got a 7200 RPM 500GB drive in at the moment, but i need two drives for the applications I run, as they prefer the open files to be on a separate physical drive to the application/OS. I currently achieve this using a 7200RPM FireWire 800 drive connected, but it's a pain having to take that with me if I want to use it elsewhere, plus the bandwidth is limiting when using other FW devices at the same time, so i'm going to remove the optical drive and mount the 2nd HDD there.

Now 500GB is massive, my install is way <100GB so something in the 120-200GB size is plenty big enough for the OS and I can use the 500GB as the data drive. But whether to get a 120GB SSD or save the pennies and get a decent spinning drive like a 250GB WD Scorpio Black ?

I know it'll boot faster, but sustained transfer rates are no different really and power consumption is generally slightly higher if anything on an SSD, is it worth spending the extra, looking for points relating to using an SSD for the OS/Boot drive really....

Ta :)