Hi
I'm using that kind of removable bays all the time
and I can tell you, that if you remove the drive
with the computer powered on, can happen 3 things
(and a sum of all, also)
1- Destroy the IDE interface of the motherboard
2- Destroy de IDE controller in the hard drive
3- Hang up the computer when it try to access
the removed drive.
IDE drives aren't design to be hot swapable so the
only secure way is to turn the power off first.
there are 2 workaround to this.
1- Use SATA drives, since sata were designed to be
hot swapable (still you need to unmount all the
partitions in use by the operating system first)
2- (What I did) buy a USB 2.0 - 5 1/4 External Drive case
and attach the removable kit inside that case,
so you can mount the drive as sda1 (same as if you
where using a usb pen drive).
when you want to take it off, simply unmount it
from the OS and power the removable bay OFF,
change the drive, turn on the bay, and mount it again.
that's it
That way you can change IDE drives without the need of switching the computer off.
hope it helps a little

lightman