If you have put your requests in already, I wouldn't worry about faxing. A lot of the resort room assigners don't even look at the faxes anymore! They just toss them because they got so many of them, they spent hours reading them!
Just be sure to have your requests noted on your reservation. I know there will be those who swear that it was their fax that got them the exact room they wanted. But....in over 15 trips to WDW, I have yet to fax a request and only one time did I not get any of my requests. But, that one time (at POP) I actually got a room that I think was better than what I had requested!