If you didn't have any other wireless card installed then you would lose your ability to use Wifi. Otherwise it's not that big of a deal. Wireless cards aren't really necessary in desktops though since you should just plug it up with an ethernet cable and be done with it.
I removed the network card , it made no difference to performance.
I am considering swapping the Radeon 6800 for an Asus ATI HD 7750, as the 6800 is giving faulty hardware warnings. Will the 7750 cover the next PCIe1 slot or will it remain free?