AI have a couple of cake orders this week and will need to use a buttercream on most of them. I have read a recipe where one can substitute shortening for butter 60:40 has any one tried this? If so what are the results.

Did a quick search online. Toba Garrett's SMBC on Epicurious ( http://www.epicurious.com/recipes/food/views/Swiss-Meringue-Buttercream-109239 ) has a note at the bottom for substituting some high ratio shortening for a portion of the butter. You might want to try her ratios and see how (and if) it works for your IMBC.