Yes, it's a scam, and a very common one. These have been around for years.
http://www.bbb.org/us/article/work-at-home-schemes-408The BBB says it all right here:
When answering such ads, you may not receive the expected envelopes for stuffing, but instead get promotional material asking for cash just for details on money-making plans. The details usually turn out to be instructions on how to go into the business of placing the same kind of ad the advertiser ran in the first place. Pursuing the envelope ad plan may require spending several hundred dollars more for advertising, postage, envelopes, and printing. This system feeds on continuous recruitment of people to offer the same plan. There are several variations on this type of scheme, all of which require the customer to spend money on advertising and materials. According to the U.S. Postal Inspection Service, "In practically all businesses, envelope stuffing has become a highly mechanized operation using sophisticated mass mailing techniques and equipment which eliminates any profit potential for an individual doing this type of work-at-home. The Inspection Service knows of no work-at-home promotion that ever produces income as alleged."
