Just tried Quinn out.
She's probably the best 1v1'er ADC in the game, with both a blind on Q and a double steroids.
Her E is only gonna be used as a gapcloser to proc her passive, so it gets maxxed last, max her W first, it really helps.
She's a great harasser thanks to her passive, it seems to have a max range but it seems to always proritize champions.
She doesn't have good scaling on any of her skills, she also has very little AoE damage, so I'd get a shiv on her.
Her ult is actually ridiculously awesome for running away, chasing down foes (The damage portion of the skill deals more damage based on the opponent's missing health, it's pretty much Riven's Ultimate with a different range.) and pushing down towers (The W gives her ultimate a gigantic passive Attack Speed buff.)
Her natural damaging combo is wait fo a passive proc, Auto attack > Q > E > Auto attack. This actually gives her better burst than most ADCs I know of.
Her passive is not all that great for farming because most of the time the targeted minion is actually high health, and like I said, it prioritizes champions so...
I've had no mana problems on her whatsoever except for when I needed to ult, which I didn't do often.
Her W Active costs no Mana but doesn't seem very useful unless you suspect a gank, but your support should ward for things like that.
Pushing potential is actually quite high with her passive damage and attack speed steroid and Q aoe. She also has higher base movespd than other ADCs I know of (330 if I'm not mistaken.) Though she seems to have low base AD, probably to compensate for the passive's bonus damage.
I don't have AD Carry runes on PBE so I just ran top lane runes on her and won my lane just fine, this is PBE we're talking about though, my Blitz went AFK (Probably internet connection problems, he did apologize before he DC'ed again) and my opponents (MF and Sona) were... Bad, to say the least.
She's an interesting ADC, I'll totally buy her once she comes out. It'll take a while to get there though.