It used to be that foreign nationals who entered on the Visa Waiver Program (VWP) could safely marry a United States citizen and apply for a green card through marriage via the adjustment of status process, even if the period of authorized stay had expired. Being able to get a green card through adjustment of status, instead of having to travel to their home countries, had many benefits for these applicants. First, most of the applicants who were out of status would have triggered a three or ten year overstay bar the moment they left the US. In order to get their visa approved at the foreign embassy or consulate, they would have had to get a hardship waiver. Additionally, because the entire adjustment of status process is handled within the United States, applicants are permitted to stay and work while they are waiting for the green card to be approved. Green card applicants who apply abroad are typically not allowed to travel to the US during the process, let alone work in the US.
This ability of visa waiver participants who had overstayed their authorized stay to successfully adjust status in the US showed leniency on the part of immigration officials. First, the adjustment of status process is discretionary; that means that USCIS officers have broad discretion in deciding whether or not to deny an AOS application and make the applicant return home. Attempting to adjust status after entering the US as a non-immigrant is, in itself, frowned upon in certain circumstances. Second, VWP visitors give up their rights to appear before an immigration judge and can be removed expeditiously (i.e. on the next flight out) if the officer so wishes (and ICE concurs).
Adjustment of Status for VWP participants
There is a trend in many local USCIS offices to no longer be so lenient with adjustment applicants who have overstayed the visa waiver program (VWP). Roughly half of US immigration offices have begun denying these cases and deporting the applicant. Further, the 9th and 3rd US Court of Appeals have held that only those VWP applicants who file adjustment of status applications prior to the expiration date of their authorized stay are not immediately deportable at the discretion of immigration officials.
If you entered the United States on the visa waiver program (VWP) and are thinking about filing an adjustment of status application, you are strongly encouraged to contact in immigration attorney before filing any paperwork with USCIS. It may very well mean the difference between an easy green card application process and a deportation.
Source: http://www.nytimes.com/2010/05/15/nyregion/15visa.html?pagewanted=2&sq=Daniel&scp=1