the fan is defective yes.. but you do`nt need to worry too much....
you`ll be buying a new mobo so you won`t have to deal with this problem for sometime..
The problem is that the fan sometimes stops working.. now the fan is there to cool the damn heatsink and if it stops the temps get so high they your fingers burn(they do trust me).. though the comp doesn`t hang or anything its better to shut down the comp and wait for sometime then restart... also dust is a major factor so you gotta keep it clean..
plus for you it might take sometime for the problem to show up like a month or a little less or even more depending on how lucky you are..
i got the sli mobo myself.. and i had this problem from day one though it wasn`t much for 2 weeks. but afterwards it hardly used to run for more than 2 mins

... though i have not had a problem with the fan not running.. you never what might happen..
so i have asked the guys at the asus service center to get me a replacement fan..
the replacement fan is bigger in size, only runs at 5k rpm(the default one runs at 8k rpm) and also is a lot quieter and better..
asus had acknowledge this problem with the chipset fan and said that the fan was defect from the factory itself..
the only prob i`m facing is that i think i`m the first guy to go to the asus service center with this problem .. so i had to explain it to them what to do and what can solve my problem.. so i hope i would get a replacement this week ..