tl;dr: What kind of person do you think, or would like to see Jenny return as?
In season 3 we saw one of the more ambitious moves from the writers of Gossip Girl. While most of the characters on the show have their ups and downs for the sake of shake-n-bake drama, it looks now, to me at least, as if they writers have been setting up the Jenny character to be used for a monomyth within the show.
The monomyth, or hero's journey, follows certain patterns that can easily be spotted in Jenny's arc. In season 1 she begins in the ordinary world (Brooklyn) and sets off for the mythical land that is the Upper East Side where she meets strange new creatures. Guarding the threshold to this land of magic and debauchery is Blair. Luckily, Lil J has Serena for a fairy godmother.
This stage of her journey draws on for the first two seasons (which focus on other story arcs), with Jenny looking in from the outside in awe of what might lie beyond. At the end of season 2, Jenny finally passes the threshold as Blair makes her the new Queen Bee.
As season 3 kicks off we see Jenny take her first stumbling steps into the unknown, blissfully ignorant that it's not what it's cracked up to be. Her guide through this stage is Eric. The mandatory challenges and temptations are thrown in her path, but in episode 7 "How to Succeed in Bassness" the writers decide to send her down a darker path for some juicy drama. In short, she fails a challenge, falls to temptation, and loses her guide (Eric). Everytime she tries to drag herself up after this, she slips a little further down.
The writers really go to town on Jenny from now on, which is quite remarkable considering how young the character is. The list from off the top of my head includes drug dealing, alienating everyone around her, getting roofied and set up to be gang raped, and being used as a scapegoat for the dramatic ending (?) of the Chuck/Blair thing. Chuck is also on a hero's journey, but that's another story.
With Jenny having hit rock bottom, this is where the monomyth sees her through her metaphorical death and rebirth. Following the traditional path we should now see her transformation and atonement. Will she use her "gift" of newfound insight to better the lives of those around her? Will she be better at side-stepping the sucker punches and schemes of certain other characters? Will she act as the moral compass for the show, calling people out on their bullshit? Will she be confident, suave, and a black belt in sarcasm? Or will the writers just lose momentum and do a Serena?
Personally I'd like to see Jenny more confident, brutally honest, witty, and laid back. I realize I basically just described a female Chuck. Go figure.