No there is a bug in arch linux arm that limits the resolution to 800x480. It happened after the first reboot in my case. In debian I can use 1080 without problems, but the screen refreshes with lag when you move or minimize windows. The rpi blog states that they have WIP to offload the x window system to the GPU. That's what I am waiting for as the slowness of the X windows is borderline unacceptable.