We also got ours today - wo hoo!!!
We first applied on 9th January. In around March time we were asked to provide more documents including Police Clearance from UK. That took a while to arrive, so we provided that just over a month ago. We didn't hear anything else from immi (apart from to wait) and then it just arrived at about midnight last night!
We didn't need to do medical checks, so it seems to vary for different people - but it looks like they have picked up those piles of papers and the Approved stamp.
Good luck to everyone else who is waiting to hear, hopefully it won't be too long!!