From AILA, 4/16/13:
USCIS has started the data entry process for H-1B petitions selected in the lottery.
Premium processing cases are being handled first and data entry for those cases should be completed by April 15.
USCIS announced on March 15, 2013, that the 15-day premium processing clock will start on April 15.
Data entry for non-premium cases will likely not be completed until sometime in May, and rejection notices for petitions not selected in the lottery will be sent out after that.
Non-premium processing cases can only be converted to premium processing after a receipt notice is issued.