Just thought I would chime in!
I've been playing this spec for about 4 weeks now I think, I started it a couple of days after the original post and levelled from 44-50 on my Shadow with it. I was previously full Infiltration and, although I loved it, was just feeling it was lacking something. One day I found myself reading the original post and just nodding along at each point, and before I knew it I was re-specced and hooked. Loved it in PvE, and in PvP the burst damage is fantastic. I'm not topping any scoreboards but just beaten my personal best when I came 3rd behind two Smashers. I can pull off those 1v1s when it matters so I know that I'm making the difference even without all that fluff damage from Madness or Rage.
Only issues I've really had have been against full Darkness/Kinetic Combat Shadow/Assasins or Darkness/Madness hybrids in full tank gear. Sometimes it's ok but there's a couple on my server who really know what they're doing there.
I did also have some problems with survivability at first so I figured I'd play around with a few things, my current build is a slight variation of the WJ spec:
Personally I just find that Insulation helps - once I'm fully geared I may re-evaluate but truth be told I've been having a blast with it. Everytime I think about giving the Darkness/Madness hybrid a go, I play a WZ in this spec and am reminded how great it is!
Thanks for the great guide!