Buttons, buttons . . .
The current Prince of Wales wears five on his sleeve. This seems to be the maximum, among the sanely dressed. From time to time I see Austrian, German and Swiss types with one pewter button on the sleeve of a jacket. It works for them. The rest of us, who are somewhat Anglocentric as conservative American menswear tends to be, are somewhere in the middle.
Brooks Brothers did two buttons for years on a casual jacket of tweed or linen and I still have a few of those in the back of my closet and it is a look that still works for many.
But the original question in this string was about 'blazers', which have a British origin in sports club (e.g. rowing) wear, and the buttons were gold-on-brass. Since the jackets were basically, low-end dress uniform jackets, they are easy to wear, hide dirt, and have the effect of sprucing up the appearance of busy people with a minimum of effort. You put one on over what-ever and you are, somehow, 'dressed'. They have become a bit of a cliche, but are too durable a fashion staple to ever really go away. Like the blue, button down Oxford cloth shirt, most of us will always have one and they will always be useful.
Whatever you think of John McCain, he did the blazer no favors by wearing a navy blue one with three gold buttons on the sleeve during his presidential bid. The main problem is that he looked like he had slept in it. Suddenly the blazer which I previously enjoyed, a three button, side vent job, with three on each sleeve, looks a little naked. These days I would probably go with four on the sleeve.
When you wear a tuxedo you don't want to be confused with the maitre d' or the pianist. When you wear a blazer, the same applies. The quality should set it apart, and the buttons should be top grade: cast brass with gold plating. Benson and Clegg in London has hundreds of patterns. A good set may cost 1/3 of what you pay for the jacket. And why not? The buttons will out last the coat many times, and you will always have a blue blazer in the back of your wardrobe for those moments when you need to look presentable in mere minutes.