Pando -
I am looking at the ILT Notes for the O8: Performance Tuning Workshop course (Part #M08298, dated March 1999), p. 10-27:

"Select INITIAL and NEXT values as integer multiples of SORT_AREA_SIZE, allowing an extra block for the segment header."

I believe this is just another example of poorly worded notes. As the above citation notes, the extra block is for the SEGMENT header, of which there is only one. Therefore, I would recommend you disregard references to the extra block.

Tycho - Pando is ALMOST right about the one temporary segment per tablespace. There is only one temporary segment created within a TEMPORARY tablespace for each instance mounting the database. So if you are in an OPS environment with three instances mounting the same database, it is possible to have up to three temporary segments in a TEMPORARY tablespace. It is also possible to have more than one TEMPORARY tablespace within a database. Consequently, if you look at V$SORT_SEGMENT, you may see more than one temporary segment listed.