With any kind of offer/promotion the key thing is to be able to monitor its effectiveness, if all of a sudden all your regulars are bringing this in then it's costing you money. The kind of thing you'd want to be able to track would look something like the below:
Where the first 4 columns are completed when the person calls to book and the last two when they ask for the bill. This back end analysis is the difference between just saying 'Loads of people used the vouchers' and knowing how the typical voucher user compares to a typical normal customer.
If for example you are getting a disproportionate number of people coming in and spending little or nothing on drinks then that makes a huge difference to the profitability of the promotion.
Obviously not every company can offer 50% off for everyone who follows them on Twitter but there is something to be said for making some kind of contact to people who follow you. Depending on the volume of followers this can either be an automated response or have a more tailored personal touch to show you've thought about what part of your offering you think the follower might be interested in.
Director of Analytics