It's a good idea to create a bin directory in your home directory and then add it. Remember that : is the separator for PATH locations and its recommended that you end your PATH with :.. This means the last place that Linux will look is the current working directory.
It is a good idea for normal users, but it is generally NOT what you want to do with root's PATH variable. If your system has been compromised, someone could plant a command (like a copy of "ls") in a directory that you may use as root. If you run that command while in that directory and you have the "." in your path, you may find that it will install a "root kit." I know, I know... That's why it's at the END of the PATH, but it's still not a good idea. Just my two cents.

Happy Hacking