Personalizando o fundo UISearchBar

Existem poucas tentativas por aí, incluindo a subclasse UISearchBar e hackear o layoutSubviewsor drawLayer:. Após o iOS 5, o melhor método é usar UIAppearance.

// Configure your images
UIImage *backgroundImage = [UIImage imageNamed:@"searchbar"];
UIImage *searchFieldImage = [[UIImage imageNamed:@"searchfield"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 5)];

// Set it to your UISearchBar appearance
[[UISearchBar appearance] setBackgroundImage:backgroundImage];
[[UISearchBar appearance] setSearchFieldBackgroundImage:searchFieldImage forState:UIControlStateNormal];