As the result of a follow up question to me from Scott on this subject via e-mail I did some additional research. My original post is not entirely correct.
A proposal was submitted to the NFPA for a change in 300-5(d) for the 2002 code. This was proposal 3-43. The proposal asked that the following wording be added to 300-5(d): "Horizontally bored service laterals shall be exempt from this requirement." Code Making Panel 3 rejected the proposal with the statement that; "Present language only addresses trenching, not boring, thus boring is already excluded from the ribbon requirement".
This indicates to me that the panel did not intend to require a ribbon above cables that were installed by boring. It aprears to me, that based on the panel comment, if you are operating under the 99 code, a ribbon would not be required for conductors installed by boring. Also note the new wording applies to all underground service conductors, not just service laterals as in the 99 code.
[This message has been edited by resqcapt19 (edited 12-05-2001).]