I always tell ATC when changing to the CTAF. In fact on the Northern rivers sector of NSW, ATC virtually always request it!
I was flying with a new hire the other day, and he politely pointed out to me that it wasn't a requirement. I told him I knew that and he looked at me like I had two heads!!!
You see rotorblades, the world has gone mad, and this is simply a subtle example of it. I very nearly collided with a non transponder VFR lighty in a CTAF (no radar coverage) recently. We were departing with a left turn after take off. We had no comms during our engine starts, and as such we heard nothing from him. On taxi we made all the broadcasts. This guy (the lighty) heard all our calls, but didn't respond because as he put it "I made the required broadcasts".
First we new of him was when we were turning into him as he called joining downwind! I kept my cool (just) and asked if he heard any of our calls, to which he responded "yep, all of em'". When I asked him if he thought it would have been a good idea to say something, I was met with silence. This is how poeple are now trained!!!
As far as the company I work for is concerned, there are certain elements in the Check and Training department that are almost pathalogically opposed to anything other than "standard" calls, ATC comms included. A recent check item included "word perfect" A/C - ATC comms. That's all well and good, but it seems to me that this "dumbing down" of the game has extended far and wide.
The term "Pending clearence" however, now that's another story. I still cringe when I hear that nonsence!