Rory from ThinkMac (again) on why capsule buttons (Mail.app) completely, totally, utterly, suck.

In capsule buttons icons are reduced significantly in size from the glorious, large 32x32 pixels OS X pioneered back down to the miserable 16x16 size commonly used in Windows. Obviously you can’t convey as much detail in 16x16 pixels and you’re working on top of a two tone background which also has design implications. You’re also not gaining any additional space by using capsules either as the buttons themselves consume the same amount of space as a regular 32x32 icon would while providing less useful visual information to the user.