I think its funny that this thread was brought up because I have had similar experiences, both with painting and music composition. The paintings I usually can remember vaguely and several times I have attempted to sketch them in waking life, however the brilliance of the "dream art" is never equaled by my hand; mostly because I am a lousy artist. I've also had dreams of playing the piano and similarly find it effortless to create new pieces; these completely allude me in waking life though, and I am forced to simply enjoy the music once in the dream. It is truly amazing how creative we humans can be when our minds are uninhibited by the logical waking state. Hopefully we can find a way to tap into this creativity.