I recently (August 2010) received an approval of an immigrant petition for a spouse of U visa holder in around five months. I had also helped in securing green card for the principal applicant. My client has consented to share his facts and case, so I will discuss briefly the facts for a better understanding and appreciation of U visa. My client was shot while working at gas station. He helped the law enforcement agencies in the investigation and persecution of the people who committed robbery or attempted to commit robbery. Initially he received an interim U visa, and later U visa. After four years on interim relief we filed for his green card which he obtained in less than six months. In between he got married and we also filed an immigrant petition for his spouse, which was also approved in less than six months.
The U visa Category
U non-immigrant visa was created with the passage of the Victims of Trafficking and Violence Protection Act (including the Battered Immigrant Women’s Protection Act) in October 2000. The legislation was intended to strengthen the ability of law enforcement agencies to investigate and prosecute cases of domestic violence, sexual assault, trafficking of alien s and other crimes violating laws of United States while, at the same time, offer protection to victims of such crimes  who may by be here illegally and hesitant to report but for this protection.
Petition for U Non-immigrant Status:
The petition  for such status can be filed either inside or outside the United States. USCIS may grant no more than 10,000 U-1 non-immigrant visas in any given fiscal year (October 1 through September 30). This does not apply to derivative family members such as spouses, children or other qualifying family members who are accompanying or following to join the principal foreign national victim.
If not admissible to enter the United States as a foreign national, an applicant for a U visa must obtain a waiver of inadmissibility through submission of a Form I-192, Application for Advance Permission to Enter as a Non-Immigrant. This waiver is adjudicated by the Vermont Service Center of USCIS on a discretionary basis, allowing the petitioner to continue with the U non-immigrant visa process.
Application Process for U-1 Non-Immigrant Visa:
U non-immigrant status cannot exceed four years. However, extensions are available upon certification by a certifying agency that the foreign national's presence in the United States is required to assist in the investigation or prosecution of the qualifying criminal activity. And after three years on U visa principal applicant can file for a green card ceteris peribus. The qualifying family members of a U-1 non-immigrant are also eligible for green card.
Impact of Removal proceedings 
Petitioners in pending immigration proceedings. An alien who is in removal proceedings under section 240 of the Act, 8 U.S.C. 1229a, or in exclusion or deportation proceedings initiated under former sections 236 or 242 of the Act, 8 U.S.C. 1226 and 1252 (as in effect prior to April 1, 1997), and who would like to apply for U non-immigrant status must file a Form I-918 directly with USCIS. U.S. Immigration and Customs Enforcement (ICE) counsel may agree, as a matter of discretion, to file, at the request of the alien petitioner, a joint motion to terminate proceedings without prejudice with the immigration judge or Board of Immigration Appeals, whichever is appropriate, while a petition for U non-immigrant status is being adjudicated by USCIS.
Petitioners with final orders of removal, deportation, or exclusion. An alien who is the subject of a final order of removal, deportation, or exclusion is not precluded from filing a petition for U-1 non-immigrant status directly with USCIS. The filing of a petition for U-1 non-immigrant status has no effect on ICE's authority to execute a final order, although the alien may file a request for a stay of removal pursuant to 8 CFR 241.6(a) and 8 CFR 1241.6(a). If the alien is in detention pending execution of the final order, the time during which a stay is in effect will extend the period of detention (under the standards of 8 CFR 241.4) reasonably necessary to bring about the petitioner's removal.
Application Process For Green card through U visa
A person admitted and physically present on U visa for three years can apply for adjustment of status to a green card holder. There is no numerical cap on U visa adjustment applications. The person should not have refused assistance to law enforcement agencies in the persecution or investigation. The principal applicant should petition on Form I-485, along with fees and supporting documentation. Immigrant petition can be filed for family member who have held U non immigrant status before. The family member who has never held U non-immigrant status has to be petitioned on Form I-929. An applicant has the burden of showing that favorable discretion should be exercised in his or her favor and hardship must be shown.
There are other remedies and options which may be available to victims of crime. But for this article we are only discussing U visa.
 Qualifying Crimes – INA §101(a)(15)(U)(iii)
 U Visa Requirements – § 101(a)(15)(U)
 Qualifying family member means, in the case of an alien victim 21 years of age or older who is eligible for U non-immigrant status as described in section 101(a)(15)(U) of the Act, 8 U.S.C. 1101(a)(15)(U), the spouse or child(ren) of such alien; and, in the case of an alien victim under the age of 21 who is eligible for U non-immigrant status as described in section 101(a)(15)(U) of the Act, qualifying family member means the spouse, child(ren), parents, or unmarried siblings under the age of 18 of such an alien.
 8 CFR 214.14