I've been on steroids several times and never gained weight. I'm a pretty active person, but often if I am sick enough to take steroids, I even take a break from working out and still don't gain weight. My face does get round (a big, albeit vain, issue for me) and if I am on it for over 5-6 months I start to lose hair. Oh, and I keep a watch out for facial hair if it's longer than a couple months.
Everybody responds differently, so don't get too worried yet! Best wishes!!!
--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
--methylpred - finally off 6/15/08, tried Prochymal in Phase III study (can't wait til it's approved!)
--started Tysabri 3/21/08, started Xifanan 5/24/08
--single mom to 10-yr-old girl