I don't think they represent any more of a risk to your network than a usb thumb drive.
That should be possible to control and lockdown, since this is a security issue in this current scenario.
(im still not sure if its possible on windows to lockdown for example hotplugging a usb device)


About the work productivity thing. Heh, guess that depends on what school of thought you come from.
I agree. Whilst productivity is an issue here, it depends how relaxed the situation is at this workplace. To be honest... (as long as its not on company machines) I dont think its 'THAT' bad if a user wants to check his email, or maybe they have some software to track their children or something, but if the users start spending time on facebook, twitter, or just surfing the net then it could be a pain.

What number of private laptops/netbooks are we talking about here anyways? A majority?
If you can lockdown the following:

- USB hotplugging &
- User being able to connect to an additional network

then i would say the security side has been taken care off, so the only thing to talk to your boss about would be productivity (if this falls under your jurisdiction).

However:

Why do they bring in their personal laptops to work? We had the issue here where temp employees would bring their unsecured laptop onto our network, put a stop to that. Its very hard to control your equipment when its not even yours.
still is the best advice regardless of private opinions!