My favorite quote on the subject:
Belief is a wise wager. Granted that faith cannot be proved, what harm will come to you if you gamble on its truth and it proves false? If you gain, you gain all; if you lose, you lose nothing. Wager, then, without hesitation, that He exists.
Blaise Pascal
First, which God? Read a little further in the Pensees and you will find that he suggests reinforcing a tentative belief by "having masses said, taking the holy water" which makes it clear that his wager is not a bet on God, but a bet on Roman Catholic doctrine. Let me ask you, would I be wagering correctly if I chose to be a Unitarian, a Jehovah's Witness, or a Jew?
Second, if there is anything an omniscient God should know, it's the contents of the human heart. Do you not think God could tell the difference between true belief and a belief concocted for the purposes of winning the "wager"??
Pascal's Wager fails because there is more than one option for belief in God -- and, for all we know, following the wrong religion offends God more than declining to follow any of them (which means that you may indeed have something to lose).