title: String.Join vs. StringBuilder: which is faster?
body: <p>In a <a href="https://stackoverflow.com/questions/585215/can-i-rewrite-this-more-elegantly-using-linq">previous question</a> about formatting a <code>double[][]</code> to CSV format, <a href="https://stackoverflow.com/questions/585215/can-i-rewrite-this-more-elegantly-using-linq/585223#585223">it was suggested</a> that using <code>StringBuilder</code> would be faster than <code>String.Join</code>. Is this true?</p>