For many companies, their project's source code is very valuable to them -- theft of the source code could be very costly. Keeping source code tightly controlled on a local network is one way to help protect it.
However, there are advantages to hosting source code externally, whether it is simply a subversion or git server hosted on dreamweaver, or a full solution like github or cvsdude.
In most of these cases, there is the possibility that an employee or other insider could access your company's full source code and history, although presumably this risk is relatively small.
Are these real fears, or should companies not worry about them and instead make use of the advantages of third party hosts?
Are there any large successful companies currently hosting their private repository on one of the third party source code management websites?