Your MAC friends are correct as this will be an awesome gaming computer and thus their MAC orientation will not be able to comprehend it and it will indeed suck... to them.
Looks good to me although I can't say about the motherboard.
The 570 is a great choice. I have an EVGA GTX570 and it has been a great card for me.
As for a keyboard I heve been looking into my first "gaming" keyboard and for me the choice came down to these two:
NCIX.com - Buy Corsair Vengeance K90 Performance MMO Cherry MX Red Mechanical 20 Key Rollover Gaming Keyboard USB - Others - CH-9000003-NA - in Canada NCIX.com - Buy Logitech G110 Gaming Keyboard USB Programmable Backlit Keys USB Audio - Logitech - 920-002232 - in Canada
I selected the Corsair in the end. The mechanical keys are not a big feature for me but I think I'll like them. I also like the aluminum construction of the Corsair. Both have backlighting which is essential for me.
For me I took the Corsair because it "seems" likre the quality of the components will be worth the extra bucks. I say "seems" because it is very new to the market and there is very little information out there and I'm putting a lot of faith in the Corsair brand name for this.
Best of luck and have fun. :)