Most of the ppl agree that after using AP, you can still work for your orignal employer without EAD. You can also extend the H1B. The I94 states your status is AOS after you use the AP, and the timeframe of legal stay is to the expiration date of AP.
But can we transfer the H1B after using AP? I didn't find any statement in the INS memo regarding transfer. However, my friend just filed his transfer after he went to work for another company because of layoff. The lawyer who help him submit the application told him it is OK to transfer the H1b even AP has been used. You can say the lawyer could be wrong, but let us wait for the result of application of my friend. I will keep you posted.