I've used buttercream several times and love it. And I've seen some pictures of cakes decorated with buttercream, and it's so smooth that it looks almost just like fondant.
How do they get it so smooth?
There are many different methods. look in the Articles section and you will find the 'Melvira method'. Also, Tonedna has a tutorial on youtube. Sugarshack has a series of DVD's (google sugar ed productions). She has a demo on her website that you can preview before buying the DVDs. Oh... and the hot spatula method. Im sure you can find that on youtube too. Just do a search for smoothing buttercream. HTH