2002 NEC, That practice is not uncommon at receptacles.
It does, however, represent two conductors for box fill when you "loop" the conductor around a terminal.
See also, Section 314.16(B)(1) Conductor Fill.
Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once.
If conductors are passing through a box from a raceway it is always better to leave a 12 inch loop, because it will save me from a code violation if I decided to cut the conductors, or "loop" them so they would be at least 6 inches long on each side of the loop.
This would, however, increase the box fill and then the box may be too small.
I always recommend the use of larger boxes so that there will be enough space for conductor fill.
Some code references concerning "so-called loop wiring" are included below:
372.12 Splices and Taps.
Splices and taps shall be made only in header access units or junction boxes.
For the purposes of this section, so-called loop wiring (continuous unbroken conductor connecting the individual outlets) shall not be considered to be a splice or tap.
372.13 Discontinued Outlets.
When an outlet is abandoned, discontinued, or removed, the sections of circuit conductors supplying the outlet shall be removed from the raceway. No splices or reinsulated conductors, such as would be the case of abandoned outlets on loop wiring, shall be allowed in raceways.
390.6 Splices and Taps.
Splices and taps shall be made only in junction boxes.
For the purposes of this section, so-called loop wiring (continuous, unbroken conductor connecting the individual outlets) shall not be considered to be a splice or tap.
[This message has been edited by Joe Tedesco (edited 01-29-2002).]