Are Sales Reps an IT security threat?

Many, if not most, employers arm their field sales folks with laptops so that they can be productive on the road, and more often than not these laptops are loaded with security software (virus protection, VPNs, encryption software, etc) meant to protect the corporate network from security threats. While this security software seems like a good idea there are instances where it may not be enough, due to the nature of the beast that is the field sales rep.
There’s a couple of fundamental issues with field laptops in general that are issues that don’t come up with corporate desktops. One is that while you can block websites and application loading when someone’s using a desktop on the corporate network, it’s trivial to just not launch the VPN and go and do, basically, anything you want to, unfettered by corporate Mom.
A more likely scenario in the case of sales reps is the checking of personal e-mail. While it’s not usually a big deal for Home Office employees to wait until they get home at night to check e-mail, if you’ve got a rep constantly on the road, they’re not likely to wait 3 or 4 days to do so. That’s especially true for reps with families, who likely use e-mail or chat to communicate with family members while they’re away.
Of course there are corporate rules against some or all of this type of behavior, but human nature being what it is, it will continue to happen, and locking laptops down even more is definitely not the answer. Right now I turn on CNBC and get a cup of coffee before I start booting up so I have something to keep me occupied while I’m entering passwords and waiting.
Sure you can scan for virus’ and rogue applications once reps get back on the network, but sometimes (as in the case of the Storm worm) that step might be too late.
What to do? I have a solution that I’d personally like to try, but so far, I’ve been unsuccessful in convincing corporate IT to let me do it. The answer of course is to let me use my Mac laptop. Since Windows based virus’ and worms don’t run on Macs, what I do on my laptop with the Mac layer on the road doesn’t threaten the network and I’d be happy to have IT control (and lock down) the Windows layer for corporate only use. I don’t need, or expect, IT support for the Mac.
This seems to me to be a good solution, but, obviously I’m missing something. What is it?