As far as i know.. which im not sure .. you can stay up to 60/90 (not sure) days in this country after your OPT expires.. till you have legal papers you cannot work. so till your H1B is not accepted you are not eligible to work..  if you step out of the country, and you get the visa you cannot come bact till Oct 2013 ( or of that year) since your H1B starts from OCT..

If you qualify for a STEM Extenstion, you are good to go for the next 17 mos. But your company should be E-verified to have your extension done..

I am telling you these on how much I know... or have researched upon.. I might be completely wrong or write.. so i would suggest you to check with someone else.. Most of these informations are there in uscis.gov.