IF you think people are gonna go to your website by typing in your URL with an added .my or .cn, then yes, you should register those extra ones. Who knows, you may miss some business if people tried going to the .my address and find nothing there, and they give up trying to find your company's website. But if its just a personal website, it's not that important to register all the different permutations of your website...

Another thing is: some people may type in a "www" in front of your address, some people will not. Example: try go to http://www.tm.net.my and http://tm.net.my. One goes to tmnet website, one just goes nowhere