Personally I like RGB (Hence my purple Corsair 460X) I think they can look good. I agree they can also look hideous.
It's interesting that 12 months ago a lot of people were complaining about 'not another red/black card/mobo/whatever' so now all manufacturers have gone to plain black pcbs with some nice RGB lighting everyone seems to have gone 'OMG so tacky/twelvie horrible'
Point is no matter what they do in the design world people will love or hate it and be vocal either way.
I will admit I chose my Z77 board based on the heatsink colour. Black and blue are a great combination. Unless you run an OC3D site. Then you want the Red black and white