I once tried a ret build, but went deep into prot for reckoning. Now you lose out on DS, and reckoning only procs from dmg done to you, but when i went a did dailys, i have to say.........this shit is scary. W/ the new SoC, the dmg i did wiped out 10-15 enemies in an instant, and in cataclysm, if nothing changes talent wise in the trees, or they don't move reckoning any further down the tree, it will be entirely possible to have a 0/25/51 build as ret, which looks like a juggernaut of a PVP build.
NOTE: Use this in a BG if you really wanna mess with someone. When a rogue is chipping away at me, and i have this spec, reckoning is almost always up. It only takes a set of charges to instagib anyone, but you have to be in the right place in the right time