Like any other business, success with SMC depends on how much you put into it, whether or not you have a clear business plan, your location, and how much money you have to invest.
Basically, once you purchase your membership, you are free to purchase products or not, depending on how you intend to sell them; after the initial expense, maintaining the membership is very inexpensive. SMC will drop ship products for you if you can generate orders via the web or their catalogs, or they'll send you products directly if you have the money up front and a place to warehouse them. You can order tons of catalogs and send them in a massive mail campaign (or pass them out), you can maintain an Internet catalog, or you can stock a brick and mortar store or sell at flea markets. You can do wholesale (to resellers) or direct retail...or any mixture of all of the above. You determine your markup (or profit margin) since you pay a rock-bottom price for merchandise.
I was pleasantly surprised by the quality of the items in SMC's catalogs, they do indeed keep updating their products and catalogs, they are things that (under normal circumstances) people would like to buy (i.e., cute knick knacks, decorative items, some furniture, etc.), and their prices were good. However, their "coaching" seemed to be little more than glorified attempts to get me to buy more products, and in the current economy it can be difficult to get people to buy things that aren't necessities (almost none of SMC's items can fall into that category).
It can work, it has the potential to work. BUT it's not going to work overnight, and it's no less work than any other job. As a matter of fact, it's probably more work since you'll basically be responsible for running your own business. There's no guarantee that it will work for you. But it can be done, and it can be fun. Good luck!