There have been several stories about the insecurity of wireless networks recently. One said that it found about 5000 wireless networks in London, more than 95% of which were insecure.
One company in the US markets software and a wireless card for a Compaq iPaq. I know, 'cos I'm going to have it demoed and borrow a loan unit for a few weeks on Wednesday. It analyses wireless network performance, security, and the like - all for less than £3000, and if you've got a compatible PCMCIA card, NetStumbler, and you like Pringles crisps, then you can do it for mostly free with your laptop.
We plan to offer a service where we go and do 2 hour audits of a customer site then fix the security issues. It's pretty straightforward if you think about it, and there are several products on the market to put VPNs on the wireless portion to ensure the right people connect to the right network.