With as little as three million and as many as twelve million infected machines, Conficker has the potential to cause a lot of havoc. It has failed to do such so far, but several security companies have warned that it has continued to update itself and the people behind the worm are seeking to expand it using its peer-to-peer function.
Good security practices will of course keep you safe. What the worm's authors are betting on is that many people do not keep their machines updated. What exactly they have in store for the millions of infected machines is anybody's guess. But even if it has failed to cause much of a stir now, there is potential for problems in the future.