How frequently do quota backlogs change and will they improve?
The U.S. State Department issues the Visa Bulletin each month (usually around the middle of the month), and it provides information that will take effect on the first day of the following month (i.e., on July 9, 2012, the DOS released the dates effective as of August 1, 2012). The priority dates in each category and for each country can change each month depending on green card availability. Be aware, though, that the priority dates can also stay the same. They can move very slowly or progress by several months or years. They can move forward or backward. There is ultimately no way to anticipate what the priority date will be in a future month or when a category will become current.

I've heard that people from India and China are the only ones subject to quota backlogs. Do quota backlogs apply to me if I was not born in either of those countries?
Yes. Quota backlogs can apply to everyone, regardless of where they are from.  In fact, the EB-3 consistently has a six year backlog for all nationalities and a 10 year backlog for Indian nationals.  In addition, a three year backlog for all nationalities in the EB-2 category, which includes applicants who are physicians, was announced in July 2012. As of this writing, visas for Indian and Chinese nationals in the EB-2 category are unavailable.

Can I get ahead on the quota backlog list?
Other than filing a petition in a higher preference category (which requires that you and/or your position meet(s) the criteria for doing so), there is no way to get ahead on the quota backlog list. You will otherwise need to wait until you are eligible to apply along with others on the list before you can move forward with filing the last step in the process (which is accomplished by filing an application to adjust your status to lawful permanent resident, or by obtaining a green card from an overseas U.S. consulate).

What is the difference between the visa category being “U” (Unavailable) and “MM/DD/YY” (quota backlog)?
“U” means that there are no more green cards available for the month. If there is a date noted, that is the cut-off date, which means there is a quota backlog. You can only move forward with the permanent resident process if your priority date is before the cut-off-date.

If my H-1B time is running out, how will my H-1B status be affected if my green card application is held up by quota backlog?
The “American Competitiveness in the Twenty-First Century Act of 2000” (AC21) allows your company, on your behalf, to apply for an extension of your H-1B visa time (in three year increments) if you have an approved I-140 yet are unable to move forward with the I-485 because of quota backlog. If you have dependents, their H-4 status can also be extended. If you are not the beneficiary of an approved I-140 petition, you may still be able to obtain extensions (in one year increments) provided the labor certification or I-140 petition have been pending more than 365 days.