Theft is never a good thing. In the context that Austin Kleon uses the words "theft" and "steal"... they are more like hipster terms for where/how you find your inspiration and creativity. Austin is really interesting. I've been following his Tumblr feed and I'm looking forward to his book "Steal Like an Artist".
People ask me where my inspiration comes from. I think it comes from the sum total of everything I see, hear, smell, feel, read, love, etc. It all goes into my brain and percolates somewhere in the dark cob-webbed corners and then comes tumbling out again when I sit down to create.
Sometimes it's good, sometimes it bad. We all strive for the good...for originality.