Pete are you talking about cables?
Right now in the 2002 code cycle only type MC is specifically allowed in a raceway. 330.10(7)
For 2002 part of section .22 of the raceway articles was changed to this wording.
XXX.22 Cables shall be permitted to be installed where such use is permitted by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.
Right now type MC is the only one I know that says it is permitted in raceways.
Previously NM, UF, SE and MC could all be in raceways.
I have heard in the 2005 code you will again be able to put these cables in raceway.
I have been told it was a case of one hand not knowing what the other was doing.
All this does not change the fact that you can and are sometimes required to put any of these cables in a "short section" of raceway for physical protection.
Another forum member asked the NFPA for an official interpretation of "short section" and the reply was less than a full length of raceway.