Charisma bonus is applied to strength/con while raging. (Example a fourteen charisma barbarian would get +2 strength and +2 con in addition to the base +4str/+4con. His rage would be +6 str/+6 con.) Negative charisma will also reduce rage bonuses using this same formula.

So, if I were a half-orc barbarian with 6 charisma, I would just lose 2 AC when I rage with no positive gameplay effect?

If so, my half-orc is going to back to charm school for another year.

You would get +2 STR/CON and the Will saving throw bonus.

Ordinarily, you'll get +4 STR/CON from a rage. The -2 modifier the 6 CHA attracts halves this.

Thanks, for some reason I had +2 to STR and CON in mind for each point that the Charisma modifier is affected.

Charm School still sounds like a good idea, though.

Well, really... if you're playing a half-orc and you choose to put those points into strength, rather then charisma you'd still be better off most of the time.

4 skill points going from charisma, into strength would raise your strength from 16--->18. When raging you'll end up with 20 strength. If you choose to boost charisma you'll have 16 strength and 20 in rage. So, if you decide not to put points into charisma you'll have +2 strength all the time, and the same strength while raging. However, I've a feeling you'd have a more interesting time playing an intimidating barbarian with charisma, then a whining craven without.