You can do this sort of thing regularly through sites like giveawayoftheday.com

Long-term results are mixed and (as henning notes) this sort of stunt does not attract the type of customer a business wants (that is, those willing to spend money on quality software).

Bogging down your support staff with a bunch of cheapskates looking for freebies can increase costs while doing squat for revenue, all while seriously cheezing off those of your customers who actually paid for your product.

If you're new and you're desperate, go for it. Otherwise, you might want to consider a different advertising strategy.