As an immigration lawyer, I regularly advise green-card holders how long it will take to sponsor their spouse, their brother, or their child for a green card. The U.S. immigration law has several categories under which a U.S. citizen, or a U.S. permanent resident (green card holder), can sponsor a close relative. All but one of these categories (the category including the spouse, child, or parent of a U.S. citizen), is subject to annual numerical limitation. The annual limitation for worldwide family immigration in 2010 is 226,000. This numerical limitation is determined annually by the U.S. State Department, in accordance with U.S. immigration law.
Because more than 226,000 family-based visa applicants wish to immigrate annually, a queue is formed in each of the family-based categories. Applicants are assigned a "priority date" that serves as their place holder in the queue. The priority date is the date that a sponsoring family member submitted the immigrant visa petition. So if a permanent resident submitted a visa petition for their spouse on April 1, 2001, the priority date for the spouse is April 1, 2001. Applicants can then view where the queue currently is by reviewing the State Department's Visa Bulletin, published monthly.
As an example, an excerpt from the July 2010 Visa Bulletin is below. The family-based immigration chart is at the bottom of the first page, and continues onto the second page. Category "2A" is the category for spouses and children of permanent residents. Under the "All Chargeability Areas Except Those Listed" column, the current priority date for category 2A is July 1, 2008. This means that if a permanent resident submitted a petition for their spouse or child before July 1, 2008, the spouse and child could now apply to immigrate to the U.S. So for persons that fall within the category of 'spouse and/or child of permanent resident", the overall timing will be around two years. The rest of the family-based chart shows some queues going back into the 1990's, and even 1989 for one category. For persons in those categories, the amount of time it takes from when their sponsor submits an application until the benefiiary can actually apply for an immigrant visa, can be up to twenty years.
http://www.scribd.com/doc/34685046/Excerpt-July-2010-Visa-Bulletin
Excerpt July 2010 Visa Bulletin
As I'm familiar with the long queues in various family-based categories, I was surprised to come across a small article in the USCIS Ombudsman's Update showing that family-based visa numbers are going unused. About 10,000 family-based visas went unused in 2009, and the Ombudsman estimated many would go unused in 2010. How can family-based visa numbers be going unused, yet the queues still remain so long? The Ombudsman attributes this in part to the fact that when visa applicants are residing in the U.S., they are not provided notice when their priority date becomes current, so they just don't know that they are finally eligible to apply for permanent residence. I think that's only part of it. The current priority dates show that U.S. citizens and U.S. permanent residents petitioned for family members long before the current recession and high unemployment. The Update does not provide data as to how many of those permanent resident petitioners have actually returned to their home countries, and no longer need to sponsor a family member. Regardless of the reason, I hope that the USCIS Ombudsman can work with the Department of State to move the priority dates faster in all categories so that more family-based visa numbers do not go unused again.