I got my ack letter last Thursday, Thank God. It was almost 8 weeks. Actually when I noticed that it was coming to 8 weeks, I was almost going to complain on Solvit website, but I gave them a last chance and started to email them every two days, asking for an update, of course they gave me automatic response, and when I noticed in the mailbox there was the green paper from the post office, so I went there straight away and it was finally from INIS. After I got my Stamp 4 they emailed me saying that they have sent the ack letter on 21/01. I was like: Really?
Anyway, I applied on 27/11/2014 and got the letter on 22/01/2015. Be prepared to wait!
@tastylentils I definitely agree with you, they must do that! There ain't no other way, really.