Quoting from:
http://www.theregister.co.uk/2008/12...you_want_macs/

The two salesman-academics ran a study which
involved giving one group of people a chocolate
truffle, and asking another group to be strong
and abstain. It appears that scoffing just one
fancy choc, according to the profs, tends to
unleash a "what the hell" syndrome. The truffle-
gobblers then feel a strong desire for more
treats - for instance ice cream, pizza, and
potato chips - while the puritanical group found
it easy to spurn any further delicious but
possibly nutritionally unwise offerings.

If that was all, frankly we wouldn't have
bothered you. But it's not.

"A second study again had people eat or resist
a chocolate truffle and asked them to indicate
how much they desired several products that are
symbols of status [for example] an Apple
computer... People who ate the truffle desired
the status products significantly more than
those who had to resist the truffle," write
Laran and Janiszewski.