I tried the Sams buttercream for the first time a few weeks ago. Honestly, I really wasn't impressed at all. It tastes like canned icing to me, nothing like homemade. Now if I know the person ordering from me just wants a cool looking cake and will order from WalMart if I don't make it for them, then I don't care to use it, because it's the same they'd get from WalMart anyway. But if it's someone that loves that homemade icing, then I'm not about to cheat them out of that.
I do notice, though, that if I color my homemade buttercream, sometimes the colors separate after a day or two, so I can't really reuse leftover icing. The Sams buttercream seems to be better about that, so right now I'm making homemade icing for the main part of the cake, and using what I have left of the Sams icing for bright or dark colored details on the cakes. I probably won't buy more, though, once this is gone.