An interesting point. As an area controller dealing with flights from Heathrow, for example, I'm not aware of any requirement to report reaching cruising level. Personally I don't have a problem with it if I'm not busy. You're quite right to say that it can clutter up a busy frequency and would most probably be considered unnecessary. I notice that you refer to reaching 'cruising' level. It probably is good practice to report reaching an intermediate level that you've been cleared to when you're looking for higher, we want to give you as continuous a climb/descent as we can. Again though, common sense should prevail, if you hear an extremely busy controller, he's probably getting to you shortly so don't hassle - and if you've been told to standby or maintain once there's a good reason, wait. Just to balance it the other way though, I am only human and there have been times when a reminder has been welcome.
