<p>Is there any reason to avoid using <code>text-align: justify;</code>?  </p>

<p>Does it reduce readability or cause problems?</p>

I prefer left justification (text-align: left) because it's generally more readable.  It's also quicker to read evenly-spaced words, so I hear.  Unless you have a stylistic reason for using justify, keep it left, right, or center.  Especially for body text, use left.  (Actually, you'd want something like "forward" for text in the other direction (e.g. Hebrew)...)