Yeah, the performance was generally terrible as the pads wore. It you didn't constantly adjust the pads in, they were unreliable as a performance brake. It didn't help that, for some ungodly reason, manufacturers decided to put the roller brakes (and u-brakes) mounted beneath the chainstay.

Cantilevers, while they have a similar issue, are nowhere near as bad.

Extra wear parts, higher maintenance, little gain...same thing that killed "parallel push" v-brakes. The cams that they use now in hydraulics work great to maintain a larger pad gap, while avoiding the drawback of pad gapping that mechanically-actuated brakes have.

[MENTION=21434]chizlr40[/MENTION] if you decide that the brakes are too much trouble to get working satisfactorily, u-brakes can be used in lieu of roller brakes with little-to-no modification.