Deals. Contests. These are is a common tactic but they make an assumption about what "working" is that's really worth discussing. Let's go...
Giving people a discount upfront sets the expectation that following you is about deals and that changes the equation from what social set out to be. It's not to say that it's a bad idea but you have to be aware of the implications... You can't lead in with "we give free stuff" and turn around and expect to have a great conversation, engagement, etc... Offers don't always matter and there's really not a lot to say about another $10 pizza coupon or request to share the page for a long shot chance at an iPad.
Facebook changed the game removing default tabs for a reason and I guarantee you "sales pages" came up many times in the internal debate to make the move. People now land on your posts... your photos... your fan's remarks... your story has to be based on more than deals to get a follow and keep people glued in for more.
I've certainly done offer based campaigns, have the conversation with brands all the time and frankly while I get the purpose and sometimes run those sorts of campaigns I'm very reluctant to make them the doorway in unless the message fits with the brand rather than the following. I also wouldn't consider offers/contrests/deals social. To me it's really bringing broadcast to a sharable platform.
If you are going to take the deal approach upfront or down the road think about the medium and purpose, not the offer book you made for your google ads. What's going to stand out. What relates to the value of your business. What will people want to share.
No matter what your campaign is you need to measure while beyond the like. Does the offer / following do anything for the business [and that's not necessarily sales... retention, learnings, discussion, all huge]? Do people who you pull in with an offer come back? For deal based campaigns, it's the "groupon" debate: you're trying to grow by giving away the shop to do it. If you aren't measuring that over the long haul you may be "growing" the number of followers and bargain seekers to the detriment of your business.
Thus we return to the basic question: what's the purpose of you being on social and how do you find success with that in mind.