Sometime in the past few hours, Twitter made a subtle, but not insignificant change: their Promoted Trends are now appearing at the top of the Trends area on Twitter.com. Previously, these were at the bottom of the area, buried under the inevitable topics about Justin Bieber. Obviously, anything at the top of a list is going to be more visible than something at the bottom of the list -- and Twitter appears to be testing out what that will mean for click-through rates of these Promoted Trends.