honestly I can't fathom the logic that says it is more respectful and/or formal to wear a monstrosity like Princess Beatrice's headgear then the pretty barrette that Samantha wore. Quite frankly it seems as if some of those hats are some sort of enormous joke being played on the people wearing them and the fashion commentators taking them serious.
Even if it wasn't your particular cup of tea, there was nothing in the slightest disrespectful or informal about the fascinator that Princess Beatrice wore. It was created for her by hat designer Philip Treacy. I read that there were at least three dozen women wearing Philip Treacy hats at the Royal Wedding, including the step-mother of the groom (Camilla, Duchess of Cornwall), the mother of the bride (Carole Middleton), Princess Michael of Kent, Queen Anna-Marie of Greece, Princess Mathilde of Belgium, and Victoria Beckham.
The bride herself has worn Philip Treacy hats many times. Camilla wore a Philip Treacy hat at her own wedding to Prince Charles.
How on earth can wearing bespoke headgear by the same designer who made the hats of the mother of the bride and the step-mother of the groom be considered disrespectful?
Here's a blog post about Philip Treacy in general: http://www.culch.ie/2009/06/03/philip-treacy-the-culchie-interview/
and about his hats at the Royal Wedding in particular: http://1001zones.com/2011/05/philip-treacy-hat-exhibition-in-royal-wedding/
Perhaps it's not the most polite thing -- on an etiquette forum particularly! -- to make a rude comment about a someone's headgear, just because its style is not to your liking.