I think they're useful for toolbars, but not normal buttons. Chalk it up to just not being use to them yet, but it's not very intuitive that a command button is a command button when it's on a form. Just my .02¢

>When those buttons first came up I read an explanation, I think from Microsoft, that went along these lines: When the design switched from 2d to 3d, objects (eg. buttons) could be better distinguished because they appear raised. However, over the time more and more controls have been added to applications, especially to toolbars. We've reached a point where 3d shapes actually distract most users according to observations. There's too much border compared to the actual button.