Daily deal sites, especially Groupon (because it is publicly traded), have gone through bunch of negative publicity recently.
However, as a practicing marketing professional, I want state explicitly that Deals (DD) is a great channel for marketers.
If you are with no marketing budget, but still entrusted with bringing in new users, DD is a great tool. The real benefit is that it does not require any upfront marketing dollars. Yes - margins can be negligible or even negative - but this is something your finance people are willing to forgive. Secretly, they are happy that you are actully bringing extra topline income. Costs be damned!
Couple of other advantages with DD that are not apparent:
(1) A significant portion of customers who buy DD coupon don't redeem. This portion is lower, the higher the deal price. 30% to 10% is a good range. Note that these customers can redeem the deal amount even after expiration (depending on state laws), but you can give apply it to the full price after expiration of the deal. This is likely be a profitable transaction.
(2) You can expect 5% to 10% in extra business from the publicity generated by DD. Many customers dont like to deal with DD sites (because they have questions etc) and they will contact you directly. The benefit with these transactions is that you don't have to pay the commission to DD sites.
You can easily account for the above factors in the DD economics calculations.
I understand that all businesses are not appropriate for DD, but if your business is, you owe it to yourself to explore this option.