I really loved this story. Excellent satire, great reading.
As for believability, here's how the neuroendocrine research stands today:
There's quite a few chemical messengers that the gastrointestinal nervous system uses to communicate to the central nervous system: orexin, cholecystokinin (CCK), pentagastrin, and some others. If these hormones could be combined with a few biochemical tricks, you could come up with a chemical that would cause the recipient to feel hungry for, say, a food with high fat content and high sodium. Making it specific for McDonald's french fries as opposed to your grandma's potato latkes isn't possible with normal foods.
One way it could be done, however, is by incorporating some antidote into the McD's food that would neutralize a modified non-degrading and super-active form of one of the above hormones. An affected consumer would then eat all salty-fatty food she could get her hand on until she hit on the McDonald's french fries. Presumably, the next time, she would know just to head straight to the McDonald's to get the antidote.
As for behavior modification darts, you could use a synthetic form of oxytocin. Oxytocin increases following mating in a monogamous vole species and is needed in these for the formation of a pair bond (i.e. after injecting oxytocin into the brain of a female vole, she will tend to prefer the company of the male she was with when she received the infusion). A similar effect in males is seen with vasopressin. Problems are
1) This hasn't been replicated in humans, so it may not apply to love
2) Oxytocin and vasopressin are released during orgasm in both voles and humans. Since people don't always fall irrevocably in love after one sexual encounter, whatever chemical was in the love-dart would have had to cause a much greater effect than what normal oxytocin would induce (And no, I don't think it's just a question of upping the binding to the oxytocin receptor. Just like pushing a button really hard doesn't make the elevator arrive any faster, increasing the binding of a synthetic form of oxytocin wouldn't always make the effect greater.)
3) Oxytocin and vasopressin have different effects outside the brain compared to inside the brain and the two are seperated by the blood-brain-barrier (BBB). To make a centrally active form of oxytocin, you'd have to figure out some trick to cross the BBB, which is not easily done with such large peptides.
I'm not sure how you'd cause someone to desire something as hideous as a SUV, but the wake-up dart is easy: caffine.