USCIS just announced that on June 11, 2012, it received a sufficient number of petitions to reach the statutory cap for FY 2013. USCIS will reject H-1B petitions subject to the cap that are received after June 11, 2012.
Last year, the H-1B cap took more than 7 months to be reached, on 11/22/11. In the year before that, the cap was reached after more than 9 months, on 1/26/11.
Please note that the H-1B cap is normally irrelevant for H-1B extensions, transfers and amendments. Generally, only H-1Bs for beneficiaries who have not received an H-1B approval previously are subject to the cap.