Poppy's a god awful jungler compared to what you see commonly.
She's best as a top laner against other ADs imo. Gangplank, Tryndamere, Jax, and Ryze are all free wins for her. She can probably handle most characters so long as the jungler is able to help out with trades from time to time, but she loses CS-wise to pretty much every AP caster that goes top that isn't Ryze.
She also apparently wins vs. Riven, or something like that.
She COULD be played in any role that's not mid-lane though. You just gotta have the right masteries/runes. Her ganks are okay, but her jungle speed is on the slow side, and support Poppy does fine so long as your AD carry is ready to follow up on wall stuns and the like. Vayne/Poppy and Kog'Maw/Poppy have worked very well for me in the past. You NEED to get kills and assists though. Once you have PhilStone, Boots, and a Sheen, things really start to take off.
You could also do a cheese set up with Blitzcrank/Poppy or Alistar/Poppy, though I've had way, WAY more success with the former.