Just tried Janna...I almost fell asleep!
Maybe it was just my team comp but holy hell was playing Janna god awfully boring. Laning was hell, I literally couldn't do anything against a Sona/Varus with a Sivir ADC who never seemed to be running ricochet or her Q, then our Shaco jungle (god I hate that champ) would come down, get caught out and I'd have to blow my load on a disengage.
I can definitely see her usefulness, her peel is amazing, but I'll be more wary in future comps. The only reason I picked her was to help with the enemy Vi which I got a few chuckles out of when she Qed into my tornado.