There’s no faster way to grow your email lists than with cool prizes and giveaways. People love free stuff. Sweepstakes are easy, and they get results. Just not always good results. You tend to get a bunch of freeloaders who were only interested in the prize. They couldn’t care less about your company. Then next month, when you send them your "real" email newsletter, they unsubscribe, or report you for spamming them (unless they won the prize, in which case they’ll wait another month before unsubscribing).
Luckily, ReturnPath has posted some tips on what kind of results you can expect from a sweepstakes-generated email list, and how you can prevent spam complaints and dismal conversion rates: