when you see really awesome piping work, like on the food network challenges, or ace of cakes, do you think they're using royal icing or butter cream? if it's royal, could you use that on buttercream? i'd like to improve my piping skills, but don't know where to start other than practice practice practice.

Do you mean piping for stringwork? If so, I'm not sure what they use on TV, but I've tried both for doing stringwork and definitely prefer buttercream simply because it's easier to work with and easier to get the right consistency. Royal icing dries out too quickly. Delicate stringwork on the side of a cake can also break when you go to move the cake, and I've found that this is more likely if you use royal icing. The buttercream is less likely to crack and break when the cake is moved.

Most if not all cakes on the Food network challenges are buttercream covered in fondant. All of Duff's (Ace of cakes" ) cakes are made the same way. The majority of the time, royal is used especially for piping and fine string work. Even decorative scrolls. Buttercream will breakdown royal icing. You can still do awesome piping on buttercream. Like you said, practice.... HTH