Hello noha and everybody

The best way to find out information on these OPT question is look at these two links
One that was published on federal registrar regarding opt rule and extension dated April 8 2008

http://edocket.access.gpo.gov/2008/E8-7427.htm

I have pointed this info here

2. Periods of Unemployment During OPT DHS regulations currently define the period of an F-1 student's status as the time the student is pursuing a full course of study at an SEVP-certified school or engaging in authorized post-completion OPT. 8 CFR 214.2(f)(5). They do not specify how much time the student may be unemployed, making it difficult to determine when an unemployed student on post-completion OPT violates the requirements for remaining in F-1 status. As status during OPT is based on the premise that the F-1 student is working, there must be a limit on unemployment, just as the F-1 student's period in school is based on the premise that he is actually pursuing a full-time course of study, and there are limits on how often the student can reduce his course load. An F-1 student who drops out of school or does not pursue a full-time course of study loses status; an F-1 student with OPT who is unemployed for a significant period should similarly put his status in jeopardy. Therefore, this rule specifies an aggregate maximum allowed period of unemployment of 90 days for students on 12-month OPT. This maximum period increases by 30 days for F-1 students who have an approved 17- month OPT period. In addition to clarifying the student's status, this measure allows time for job searches or a break when switching employers.




Another question and answer provied on april and  May 2008 has some additional info

link: http://www.uscis.gov/files/article/OPT_4Apr08.pdf
Link : http://www.uscis.gov/files/article/supplemental_opt_052308.pdf