What status do I get while application for RPI immigration is pending?

The short answer is that almost all undocumented aliens who are in the United States illegally, while their RPI immigrant visa status applications are being processed by the USCIS, they will have no legal status, and since the applications might take months, or even years, to be approved, they will continue to experience misery of being without papers.  During the waiting period after filing the paperwork, the immigrant will not be able to work legally or travel out of the country or apply for driver's licenses or do any of the other things that RPI status holding immigrants will be allowed to do.  It is too early to predict it but maybe some states might allow them some privileges merely on the basis of having proof of submitting an application.  I am optimistic, though, that once the Obama Comprehensive Immigration Reform is signed into law, chances are that unless you commit a deportable offense, you will not be harassed just for being in the country without any legal status.  Be prepared though for months or even years of wait as the USCIS is forced to process millions of applications in a time of government austerity.