It spins down regularly enough.
Saying that, I have swapped my system around. I've now put the SSD in to the OptiBay and the hard disk where it 'should' be.
Main reason is the 7200RPM Seagate drive I'm using vibrates a little, and I can feel it where it was on the right hand side. I can't feel it when it's in the hard disk bay.
In terms of battery life - I still had over 4 hours from it yesterday arvo which was a bit of a surprise. I'm guessing though cos I'd copied the stuff I was working on to the SSD, and the drive had spun down.
Even so, it's pretty impressive.