I've been pushing for switching all saves to a 1d6-only roll, but now I'm reconsidering. A current post on Delta's D&D Hot Spot linked to an older post on granularity of checks. Normally, I don't worry that much about granularity -- I tend to go with large chunks -- but there's a certain point here that a potentially dangerous outcome that hinges on a die roll, like the "to hit" roll and save vs. poison, should have higher granularity.
On the other hand, I still like the idea of the damage roll also being the saving throw. But maybe I'll give that up for PCs. I'd still handle item saves with d6 damage rolls, where applicable, and would also use the d6 for acquisition rolls (learning new languages, weapon training) and perhaps non-critical saves. So, I'd still write ability scores like "13 (4)", to indicate values on both a d20 scale and a d6 scale.