Re: Iron Skin & Natural Resistance worth it??
Iron Skin, as a rule, is inferior to Shout past a single hard point. Shout gets the same per-level bonus yet affects the entire party. It may require occasional casting, but since Battle Orders and others do, as well, it's usually not a problem, especially with the time synergies. If you're not a Concentrate build and need more defense, look into gear before spending limited, unretrievable resources like skill points, and then spend those in Shout first. Frenziers can use Taunt, which reduces non-boss attack rating and effectively makes you harder to hit, to synergize their main attack, so there are usually other ways to get what you need.
As for Natural Resistance, it was much more important in pre.10 builds which focused on magicfinding or all-out damage gear (almost exclusively for dueling). Now, I'd say there are other ways to get resistances, but - unlike defense - you really can't give up much to get something else. An extra point or two helps very nicely make up for what gear lacks, assuming you can spare the points and aren't looking for better resistances elsewhere. You really don't want to put excess points into it if trading for an higher Annihilus and/or Hellfire Torch winds up getting you what you need, as you'll end up regretting it later.
