I am so glad I stumbled on to this thread. I too was in a similar situation - mailed mine, and my wife's, visa applications on Sep. 3rd, they received them on Sep. 4th, but I haven't yet received any email that they have opened the envelope.
I have an HSMP approval letter, so I was just applying for entry clearance for the both of us. We're traveling on the 17th, and I was getting very nervous about getting the visa on time.
Like an earlier poster suggested, I called A Briggs. They are going to pull the applications today, and resubmit on Thursday for (hopefully) same day approval (I guess the LA consulate is closed tomorrow for 'training').
I'll happily pay the $165 each for my wife and I for some peace of mind!