Holds are tough to predict from year to year.
Sometimes the best estmates for Holds are actuals from the previous year. Check out the CBS Sortable Fantasy baseball Statistics for past Hold data.
Rotorank has a set of formulas we used to predict Holds, usually based off of WHIP, ERA, and Innings itched...
I just updated the Quality Starts and Holds categories for Rotorank 2009.
I hope that answers your questions...
Thanks,
Gerry