I discovered something interesting last night regarding the critical rage enhancement. After some testing, i found that it does indeed have it's effect doubled by improved critical for thrown weapons, at least for the nightforged spike and a generic throwing axe. It does not have its effect doubled for two handed weapons, at least not greataxes or mauls. Didn't test single handed melee weapons, but i suspect it would't work for those either. I shouldn't have gotten so excited by the idea of a 32 crit factor (13-20 x5) deathnip barb.
What's up with that? How long have you been using this build? Did this work before they did the fixes for thrower crit enhancements?