HipRock, Okay this is really crazy for me, I was also waiting for my receipt that I had never got. April 28th, my lawyer told me the check had been cashed. I waited for receipt. Today, May 20th, finally I got my receipt, not from my lawyer but from my employer. The first mail was returned to the sender and USCIS re-mailed it to my employer instead of my lawyer. So, I don't know what happened, there was no mistake with my lawyers address. Along with the reciept, there was a paper with a request of change of address. I haven't got to talk to my lawyer yet, which I will do tomorrow, but may be something like me happened to you too.

BTW, it was premium/masters/California. The reciept date is April 22.