isoChron said:There is a feat in epic level handbook that's called Greater Iron Will or so.
Prerequisites: Iron Will
It gives a bonus of +4 INSTEAD of +2 from Iron Will.
So Iron Will seems not to stack (who would wait till epic and take it then if he could have double iron will at 9th level ...?).
Everything I've seen about the epic rules seems to indicate that balance is a strictly optional extra at those levels. Therefore, saying that something is bad because it invalidates the ELH isn't a particularly great argument.
Like the others have said, nothing will be broken by allowing people to take Iron Will (or Great Fortitude) multiple times. So what if someone can boost their Fort to sky-high levels? They're still vulnerable to getting bashed to death, fireballed to death, drained to death, or held and then coup-de-graced to death (CDG Fort save DCs tend to be astronomical). Danger comes in many forms in D&D, and you can't be invulnerable to all of them, even with this rule change.