While its true that being certified does not necessarily make you a good sys admin, it still couldnt hurt you.
If you have only a year or two of experience in the field, and are out looking for a new position, a certification can help show a potential employer that you are worthy of consideration.

Unlike Novell or MS, Unix certification is by no means required to land a good job... I hold no certifications, and have had no trouble finding good sys admin positions.

Like Neo said, the best thing to do is just learn what you are interested in... the availability of free/inexpensive OS's such as Linux, *BSD, Solaris, etc. will help you tremendously in this goal!

Good luck, and have fun!