I wish I could get sharp and clean edges like this:
http://www.flickr.com/photos/gracefulcakecreations/2896120887/in/photostream
but How?!!! 
Three words! Sugar Shack DVD!!!!!
If you go to www.sugaredproductions.com and order Perfecting the Art of Buttercream she teaches you how to get those super duper sharp edges on rounds and squares with BC. It's the best cake DVD I've ever owned! I have almost all of her DVDs but that is a must have.
Might as well order more than one if you're going to pay shipping so my recommendations for next in line would be:
Stacking
Topsy Turvey or Flawless Fondant those are both a close second
Like I said the rest are also awesome but these DVDs totally changed my decorating skill level.
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