Regular "american" buttercream doesn't *have* to be refrigerated (unless you use a perishable filling), but I prefer to as it makes them more stable for transport as it makes the icing & cake firm. It should be served at room temp, though.
I refrigerate cakes with fondant and royal icing all the time and have never had a major problem. You just have to take into account the ambient humidity level. For example, I had a cake I was doing delicate piped royal icing embroidery that was going to be painted in gold. It was July, and the cakes had been refrigerated after being iced, so they did start to sweat. I just had to wait a while for them to euqilibrate & the condesation evaporate so the royal icing could dry to be painted. Then I refrigerated it again and there were no problems. I have refrigerated many fondant cakes, too, and again, if it is *really* humid they do sweat quite a bit and get sticky, so you have to account for that if you have more work left to do on them, and it does make it slightly more trouble to cut & serve, but if you have a good sharp knife and dip it in hot water & wipe it off often, it's not really a problem.
I do try to avoid refrigerating larger gumpaste flowers for fear of them "wilting" if they get to much condesation. I suppose if you had really dark colors bleeding could be a problem if the humidity is excessive with any type of icing.
*Oops, didn't notice this was an old thread that had taken a different dirrection
Edited by CakesByJen2 - 1/8/13 at 6:35am