From Brecht:
3D View: add shift+Z shortcut key to switch to Rendered draw mode.
This was added in r59880 – grab a build from builder.blender.org or graphicall.org later than that revision to have the hotkey – it’ll be in 2.69 official too if you feel like waiting.
since I started using cycles it was 1 of the first thing I set up by myself.what could also be useful is some shortcuts for pause and resumethe render