Same here - my Whatsapp profile pictures not showing. I had the same problem happening after I upgraded to iOS 6 this morning. I use an iphone 4G. At least I know I'm not alone.
My suggestion is to send whatsapp your application debugging information so that they can come out with a fix ASAP. I have already sent them mine.
To send whatsapp your application debugging information, go to whatsapp > settings > about > contact us > and type the problem in, e.g. "Whatsapp profile pictures not showing after I upgraded to iOS 6" . Do NOT press "Have you read the FAQ yet". Instead click Done. If you have any privacy concerns, you will have a chance to review all the information before it sends. I'm no expert but it SEEMS quite harmless, it just tells them what operating system you use etc.
Hopefully if enough people do this they will fix this "Whatsapp profile pictures not showing" problem. Its really annoying.