Since the introduction of USB ports in 1996, we have seen the introduction of just about any device one can imagine being offered with a USB port connection. Since then as most of us know, you should right click on the USB icon and select "Safely remove hardware" before removing the device.. Do we need to do this?
Do I do this? No.... I don't - but I have valid reasons why I don't and I have yet to have something go wrong go wrong go wrong (USB keyboard unplugged with our "Safely remove hardware ;-))
Here is my thinking on the issue.
For any devices that does not transfer files - unplug anytime - my experience is that you should not unplug and plug in too quickly, as you need to give the PC time to recover from the abuse! I have yet to have this action corrupt software drivers, the Windows system or damage the hardware.
However for USB thumb drives, USB external hard drives or any device that transfers files on the USB port, I suggest you be a little more careful.
Often USB drives have caching enabled to improve the file transfer (default is off) - to change this:
Go to "My Computer" right click on the removable USB drive, click on "Properties" select the "Hardware" tab, select the USB drive and again click on "Properties". Click "Change Settings" then click the "Policies" tab, and change the selection to "Quick removal". This is based on a Windows 7 system, but Vista and XP are very similar.
Now with Caching off, and Quick removal on, the USB drive will not be working when you have finished a transfer, the file activity should stop and the device will be ready to be unplugged. Use a little common sense, if the drive is busy don't touch it - also if you have just backed up your PC onto an external hard drive, use the "Safely remove hardware" option that Windows recommends.
The following examples of USB devices should be fine to remove at any time:
3G external adapters
I would use caution and common sense on removing the following USB devices:
Printers (might be busy transferring files for print)
There you have it, most times don't stress about it, but be careful when transferring files.