Pretty easy, depending on the laptop. Don't let the keyboard unscrewing scare you, for most I have seen that won't be needed. Usually it's one screw on the bottom to remove the drive, then 4 screws to remove the drive from the caddy/mount, then reverse the process to install. It was so easy that when my fiance's laptop took a crap on a business trip in China, she was able to do it in minutes after a quick call to me to explain what needed to be done. She is NOT a hardware type, but she was still able to do it with minimal instruction.
\Dan