I-130 for Mother: How long does it take to get approved?

[floating]

Hello Everyone,
I applied for my Mother for GC with I-130 back in Dec 2010. Got the NOA 7 days later. I have not heard anything since.
How long does it take now to get I-130 approved for Parents of a US citizen ?
Please share your knowledge/experience.
Thanks.

 

[floating]

Sorry for not mentioning those points.
I am US citizen and my mother is abroad at this time. But she visited USA 3 times, with visitor's visa, and left on time.
However, I just got an email from USCIS about the petition.
It says, Request for Evidence:
On May 20, 2011, we mailed a notice requesting additional evidence or information in this case I130 IMMIGRANT PETITION FOR RELATIVE, FIANCE(E), OR ORPHAN.
I am waiting for the letter.
Any Idea what kind of evidence they usually ask for?
With the petition I sent:
1. My citizenship certificate
2. My birth certificate
3. My mother's birth certificate

Thanks.

 

[nkm-oct23]

Sorry for not mentioning those points.
I am US citizen and my mother is abroad at this time. But she visited USA 3 times, with visitor's visa, and left on time.
However, I just got an email from USCIS about the petition.
It says, Request for Evidence:
On May 20, 2011, we mailed a notice requesting additional evidence or information in this case I130 IMMIGRANT PETITION FOR RELATIVE, FIANCE(E), OR ORPHAN.
I am waiting for the letter.
Any Idea what kind of evidence they usually ask for?
With the petition I sent:
1. My citizenship certificate
2. My birth certificate
3. My mother's birth certificate

Thanks.

Does your birth certificate have your complete legal name AND your mother's complete legal name?

 

[I-130Filer]

However, I just got an email from USCIS about the petition.
It says, Request for Evidence:
On May 20, 2011, we mailed a notice requesting additional evidence or information in this case I130 IMMIGRANT PETITION FOR RELATIVE, FIANCE(E), OR ORPHAN.
I am waiting for the letter.

Any update on your RFE?