If you need a curved or diagonal guide, create it using a path. Paths are going to solve a lot of problems and limitations found in the 1.0 release. Option-click to view on the mask. Control-Click toggles a masks visibility. Alt-click toggles showing the mask by itself.
Paths take up less space in an image file than a selection saved to a channel.
Paths take up less space in an image file than a selection saved to a channel. Option clicking the Eye icon of a layer hides all the others. Pressing the Shift key when clicking the left mouse button on a layers eye icon will turn off the visibility of all the other layers. Doing the same thing again will turn them all back on again. Note that if a layer was not visible originally, it will be when you turn on all the layers visibility with the second Shift-click.