I think the hardest part of weaning isn't the half-life and how long it's actually in your system. In my experience the hardest part of weaning is getting my own adrenal glands to start up again. That's the cause of mood swings, nausea, rash, exhaution, etc. that I get when I stop taking steroids.
--40 year old female, dx as UC in '04 (1st symptoms in '03), switched to Crohn's in '05, 1 fistula, crohn's colitis, limited to large intestine
--rejected (reaction/didn't work): Asacol, AZA, 6-MP, MTX, Remicade, Humira, prednisone
--stuck on methylprednisolone, tried Prochymal in Phase III study (can't wait til it's approved!)
--started Tysabri 3/21/08
--single mom to 10-year-old girl