I am using the latest OS X Bitcoin Client and it creates receiving accounts itself. I don't like that. Can I disable it?
This is the intended behavior. All the clients create receiving addresses. No one knows what they are unless you publish or hand them out.
How would you create receiving addresses if the client didn't create them?
To answer your question: No, you cannot disable it.
I understand the problem however. The client (at least under OSX, which is what I use) seems to automatically create a new Receiving address every time it is run, if you do not have an unlabeled address already in your Address Book.
The reason is that you're "supposed to" create a separate receiving address for every person/entity you receive coins from. So, the assumption the client is making is that if you've labeled an address, that address is now in use, and it should create another one for you to use for your next person/entity.
To "disable" this behavior, just leave one address unlabeled. It won't create another one. Then you can manually create new addresses and label them.
Of course, I just tested the above, and it didn't work as I describe. So, I'm not sure of the behavior you're mentioning. I now have 5 addresses, all of which are labeled and the latest client (0.3.23) isn't creating new addresses automatically.