Some people buy their electronics as a "fashion statement". If you're that superficial, then yeah, maybe you'd be embarrassed to have an iPhone 4 because right now bashing the iPhone 4 is the "cool thing to do".
However, if you bought an iPhone 4 for the features, I don't see how you would have anything to be ashamed of. I've been using my iPhone 4 for two weeks now and I've loved every minute of it. When someone asks if it's the new iPhone, I say "hell yeah it is". Who cares what anyone else thinks?