Oscar definitely gained weight while he was on pred (in this case he was underweight so we considered that a plus). He also went a bit mean. We've had big problems with aggression toward his younger brother ever since he went on - even though he's off the pred, he learned this bullying behavior and we're still trying to work it out of him. It also (most likely) is responsible for the calcium oxalate stones he just had to have removed from his bladder.
I don't think we had a choice in Oscar's case (we were fighting asthma so options were limited) but he's a completely different cat since he started on pred and, even though he's off now, a lot of those changes took root.
I'm not sure about alternatives for pain - my vet uses Metacam which has it's own issues, but I wouldn't use pred if you didn't have to!
Storm (beeps and has a pink nose and toes),
Misty (with big blue eyes and tasseled ears),
Anya (only ever called Honey - she's that sweet),
Zander (who goes by Punkin' cause he's almost that bright)
Kasee (couch potato who thinks she's a dog)