Sorry, I must interject a strong protest to your comment there, Free Rider.
As a food stylist who does lots of editorial work for many different magazines, I have to let you know that we do NOT, for the most part, put anything on the food that is inedible to make the food look better.
Those fancy cookies that you see in the holiday issues are completely edible. Very often, I donate the leftover desserts, cakes, truffles, cookies, etc. to my local community theater and Meals on Wheels.
Yes, we do sometimes use fake ice cream and paint poultry to get that perfectly roasted look, but those, by far are the exception to the rule.
We rely predominently on the skill of the photographer, art director, prop stylist and our own persnicketyness to get those pretty pictures.
As for your question about cookie frosting, Pastrycake, I use royal icing to decorate my cut out cookies-although I make it a little differently than most. Buttercream tastes delicious, but it doesn't really set up and become solid like royal does.
Most recipes call for combining egg white powder and water, whipping it to a froth, then adding confectioners' sugar and whipping it until stiff. You then thin it out with water to get that smooth glazed look, and adding more sugar to get to a piping consistency. This works great-check out Martha Stewart's website for a good workable recipe.
My only problem with this process is that the frosting becomes rather dull and flat-looking when dry.
I use fresh eggwhite, and with a paddle attachment on my mixer, beat in confectioners' sugar very slowly, about a 1/4 cup at a time until I get the consistency I want--looser for glazing, then more sugar for a stiffer, pipable frosting. This way there is no added water that softens your cookie and significantly delays the drying process. Also, when dry, the result remains beautifully glossy.
I know, I know, people are afraid of the salmonella present in raw eggs. This concerns me too, but my hunch is that something about the high ratio of sugar to egg white prevents the growth of the bacteria. I know of no case of someone becoming sick from eating a sugar cookie with royal frosting. I also tend to think that most of the salmonella and campylobacter carried in eggs is present in the yolk with its high fat content, not the white. Of course, I'm no scientist and I'm just talking out of my hat, but I make dozens of these cookies every year and send them off to all my relatives and have had no complaints of sickness from eating them.
Good luck and happy holiday baking!!!