Add border.type property to QML2's Rectangle to specify border behavior/placement (inner, outer, aligned, odd-shifted-0.5-pixel)

Rectangle {
    id: intuitiveRect
    width: 8; height: 8
    border.color: "gray"

    Rectangle {
        id: centeredRectangle
        anchors {
            fill: parent
            margins: 2
        }
    }
}

Rectangle {
    id: outerBorderWorkaround
    width: 9; height: 9
    border.color: "gray"

    Rectangle {
        id: centeredRectangle
        anchors {
            fill: parent
            leftMargin: 3; topMargin: 3
            rightMargin: 2; bottomMargin: 2
        }
    }
}

Rectangle {
    id: innerBorderWorkaround
    width: 7; height: 7
    border.color: "gray"

    Rectangle {
        id: centeredRectangle
        anchors {
            fill: parent
            leftMargin: 3; topMargin: 3
            rightMargin: 2; bottomMargin: 2
        }
    }
}