Major Description
There's especially one group of methods you should overload with StringBuffer (or Appendable in a special JDK5 Class?):
StringUtils.join
It should take a StringBuffer (/Appendable) as first Argument to which the Strings will be added.
Usage Example:
StringBuffer sql = new StringBuffer("SELECT * FROM foo WHERE bar IN (");
StringUtils.join(sql, bars, ", ");
sql.append(") AND bar NOT IN (");
StringUtils.join(sql, noBars, ", ");
sql.append(");");