For some dumb reason the JSF dataTable component does not understand Sets. However Seam's @DataModel annotation *does*.
I would cool if JSF supported java.lang.Iterable as well.
(It's importance can't be estimated without C#'s "yield return" statement though)
Anyway custom DataModels for those interfaces are welcome in Seam.
I think at least one member of the EG has admitted this was a mistake so perhaps it will be solved :)