Is it possible to stop and disable (or even remove) the "this device can now be safely removed from the computer" message?
This is because I have to click the OK button everytime and I am testing about 200 thumb drive (USB Flash drive) and it has become quite annoying.
If you put the device in "quick removal" mode (it is likely already set, see this old answer of mine for instructions on how to check it and change the mode) you can just remove the usb stick without having to do the safely remove hardware every time beforehand.
Your screenshot seems to be from Vista or perhaps Win7. As Kevin mentioned in his comment above, you shouldn't even see a modal dialog if you left-click the Safely Remove tray icon once and eject the drive from the device list (only a balloon tooltip should be displayed).
Optimising drives for Quick Removal is a possibility, but not really feasible when there are ~200 drives involved. If you want an easier and quicker way to eject USB drives, use Uwe Sieber's RemoveDrive or one of the alternatives mentioned here.
