Will adding an HDD to my SSD setup, slow things down?

Solution
No, just store your os and the apps you want to speed up on the SSD and they'll load just as fast as before, and put your documents on the HDD.

Jaxem

Honorable
As long as you keep the SSD on top of the boot order it won't slow down the boot, and it will only slow down something inasmuch as it needs to access the HDD (if an application accesses things on the drive it will be slower, like itunes accessing music)